/*
 * Freescale GPMI NAND Flash Driver
 *
 * Copyright (C) 2008-2011 Freescale Semiconductor, Inc.
 * Copyright (C) 2008 Embedded Alley Solutions, Inc.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
#include <linux/delay.h>
#include <linux/clk.h>
#include <linux/slab.h>

#include "gpmi-nand.h"
#include "gpmi-regs.h"
#include "bch-regs.h"

static struct timing_threshold timing_default_threshold = {
        .max_data_setup_cycles       = (BM_GPMI_TIMING0_DATA_SETUP >>
                                                BP_GPMI_TIMING0_DATA_SETUP),
        .internal_data_setup_in_ns   = 0,
        .max_sample_delay_factor     = (BM_GPMI_CTRL1_RDN_DELAY >>
                                                BP_GPMI_CTRL1_RDN_DELAY),
        .max_dll_clock_period_in_ns  = 32,
        .max_dll_delay_in_ns         = 16,
};

#define MXS_SET_ADDR            0x4
#define MXS_CLR_ADDR            0x8
/*
 * Clear the bit and poll it cleared.  This is usually called with
 * a reset address and mask being either SFTRST(bit 31) or CLKGATE
 * (bit 30).
 */
static int clear_poll_bit(void __iomem *addr, u32 mask)
{
        int timeout = 0x400;

        /* clear the bit */
        writel(mask, addr + MXS_CLR_ADDR);

        /*
         * SFTRST needs 3 GPMI clocks to settle, the reference manual
         * recommends to wait 1us.
         */
        udelay(1);

        /* poll the bit becoming clear */
        while ((readl(addr) & mask) && --timeout)
                /* nothing */;

        return !timeout;
}

#define MODULE_CLKGATE          (1 << 30)
#define MODULE_SFTRST           (1 << 31)
/*
 * The current mxs_reset_block() will do two things:
 *  [1] enable the module.
 *  [2] reset the module.
 *
 * In most of the cases, it's ok.
 * But in MX23, there is a hardware bug in the BCH block (see erratum #2847).
 * If you try to soft reset the BCH block, it becomes unusable until
 * the next hard reset. This case occurs in the NAND boot mode. When the board
 * boots by NAND, the ROM of the chip will initialize the BCH blocks itself.
 * So If the driver tries to reset the BCH again, the BCH will not work anymore.
 * You will see a DMA timeout in this case. The bug has been fixed
 * in the following chips, such as MX28.
 *
 * To avoid this bug, just add a new parameter `just_enable` for
 * the mxs_reset_block(), and rewrite it here.
 */
static int gpmi_reset_block(void __iomem *reset_addr, bool just_enable)
{
        int ret;
        int timeout = 0x400;

        /* clear and poll SFTRST */
        ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
        if (unlikely(ret))
                goto error;

        /* clear CLKGATE */
        writel(MODULE_CLKGATE, reset_addr + MXS_CLR_ADDR);

        if (!just_enable) {
                /* set SFTRST to reset the block */
                writel(MODULE_SFTRST, reset_addr + MXS_SET_ADDR);
                udelay(1);

                /* poll CLKGATE becoming set */
                while ((!(readl(reset_addr) & MODULE_CLKGATE)) && --timeout)
                        /* nothing */;
                if (unlikely(!timeout))
                        goto error;
        }

        /* clear and poll SFTRST */
        ret = clear_poll_bit(reset_addr, MODULE_SFTRST);
        if (unlikely(ret))
                goto error;

        /* clear and poll CLKGATE */
        ret = clear_poll_bit(reset_addr, MODULE_CLKGATE);
        if (unlikely(ret))
                goto error;

        return 0;

error:
        pr_err("%s(%p): module reset timeout\n", __func__, reset_addr);
        return -ETIMEDOUT;
}

static int __gpmi_enable_clk(struct gpmi_nand_data *this, bool v)
{
        struct clk *clk;
        int ret;
        int i;

        for (i = 0; i < GPMI_CLK_MAX; i++) {
                clk = this->resources.clock[i];
                if (!clk)
                        break;

                if (v) {
                        ret = clk_prepare_enable(clk);
                        if (ret)
                                goto err_clk;
                } else {
                        clk_disable_unprepare(clk);
                }
        }
        return 0;

err_clk:
        for (; i > 0; i--)
                clk_disable_unprepare(this->resources.clock[i - 1]);
        return ret;
}

#define gpmi_enable_clk(x) __gpmi_enable_clk(x, true)
#define gpmi_disable_clk(x) __gpmi_enable_clk(x, false)

int gpmi_init(struct gpmi_nand_data *this)
{
        struct resources *r = &this->resources;
        int ret;

        ret = gpmi_enable_clk(this);
        if (ret)
                return ret;
        ret = gpmi_reset_block(r->gpmi_regs, false);
        if (ret)
                goto err_out;

        /*
         * Reset BCH here, too. We got failures otherwise :(
         * See later BCH reset for explanation of MX23 handling
         */
        ret = gpmi_reset_block(r->bch_regs, GPMI_IS_MX23(this));
        if (ret)
                goto err_out;


        /* Choose NAND mode. */
        writel(BM_GPMI_CTRL1_GPMI_MODE, r->gpmi_regs + HW_GPMI_CTRL1_CLR);

        /* Set the IRQ polarity. */
        writel(BM_GPMI_CTRL1_ATA_IRQRDY_POLARITY,
                                r->gpmi_regs + HW_GPMI_CTRL1_SET);

        /* Disable Write-Protection. */
        writel(BM_GPMI_CTRL1_DEV_RESET, r->gpmi_regs + HW_GPMI_CTRL1_SET);

        /* Select BCH ECC. */
        writel(BM_GPMI_CTRL1_BCH_MODE, r->gpmi_regs + HW_GPMI_CTRL1_SET);

        /*
         * Decouple the chip select from dma channel. We use dma0 for all
         * the chips.
         */
        writel(BM_GPMI_CTRL1_DECOUPLE_CS, r->gpmi_regs + HW_GPMI_CTRL1_SET);

        gpmi_disable_clk(this);
        return 0;
err_out:
        gpmi_disable_clk(this);
        return ret;
}

/* This function is very useful. It is called only when the bug occur. */
void gpmi_dump_info(struct gpmi_nand_data *this)
{
        struct resources *r = &this->resources;
        struct bch_geometry *geo = &this->bch_geometry;
        u32 reg;
        int i;

        dev_err(this->dev, "Show GPMI registers :\n");
        for (i = 0; i <= HW_GPMI_DEBUG / 0x10 + 1; i++) {
                reg = readl(r->gpmi_regs + i * 0x10);
                dev_err(this->dev, "offset 0x%.3x : 0x%.8x\n", i * 0x10, reg);
        }

        /* start to print out the BCH info */
        dev_err(this->dev, "Show BCH registers :\n");
        for (i = 0; i <= HW_BCH_VERSION / 0x10 + 1; i++) {
                reg = readl(r->bch_regs + i * 0x10);
                dev_err(this->dev, "offset 0x%.3x : 0x%.8x\n", i * 0x10, reg);
        }
        dev_err(this->dev, "BCH Geometry :\n"
                "GF length              : %u\n"
                "ECC Strength           : %u\n"
                "Page Size in Bytes     : %u\n"
                "Metadata Size in Bytes : %u\n"
                "ECC Chunk Size in Bytes: %u\n"
                "ECC Chunk Count        : %u\n"
                "Payload Size in Bytes  : %u\n"
                "Auxiliary Size in Bytes: %u\n"
                "Auxiliary Status Offset: %u\n"
                "Block Mark Byte Offset : %u\n"
                "Block Mark Bit Offset  : %u\n",
                geo->gf_len,
                geo->ecc_strength,
                geo->page_size,
                geo->metadata_size,
                geo->ecc_chunk_size,
                geo->ecc_chunk_count,
                geo->payload_size,
                geo->auxiliary_size,
                geo->auxiliary_status_offset,
                geo->block_mark_byte_offset,
                geo->block_mark_bit_offset);
}

/* Configures the geometry for BCH.  */
int bch_set_geometry(struct gpmi_nand_data *this)
{
        struct resources *r = &this->resources;
        struct bch_geometry *bch_geo = &this->bch_geometry;
        unsigned int block_count;
        unsigned int block_size;
        unsigned int metadata_size;
        unsigned int ecc_strength;
        unsigned int page_size;
        unsigned int gf_len;
        int ret;

        if (common_nfc_set_geometry(this))
                return !0;

        block_count   = bch_geo->ecc_chunk_count - 1;
        block_size    = bch_geo->ecc_chunk_size;
        metadata_size = bch_geo->metadata_size;
        ecc_strength  = bch_geo->ecc_strength >> 1;
        page_size     = bch_geo->page_size;
        gf_len        = bch_geo->gf_len;

        ret = gpmi_enable_clk(this);
        if (ret)
                return ret;

        /*
        * Due to erratum #2847 of the MX23, the BCH cannot be soft reset on this
        * chip, otherwise it will lock up. So we skip resetting BCH on the MX23.
        * On the other hand, the MX28 needs the reset, because one case has been
        * seen where the BCH produced ECC errors constantly after 10000
        * consecutive reboots. The latter case has not been seen on the MX23
        * yet, still we don't know if it could happen there as well.
        */
        ret = gpmi_reset_block(r->bch_regs, GPMI_IS_MX23(this));
        if (ret)
                goto err_out;

        /* Configure layout 0. */
        writel(BF_BCH_FLASH0LAYOUT0_NBLOCKS(block_count)
                        | BF_BCH_FLASH0LAYOUT0_META_SIZE(metadata_size)
                        | BF_BCH_FLASH0LAYOUT0_ECC0(ecc_strength, this)
                        | BF_BCH_FLASH0LAYOUT0_GF(gf_len, this)
                        | BF_BCH_FLASH0LAYOUT0_DATA0_SIZE(block_size, this),
                        r->bch_regs + HW_BCH_FLASH0LAYOUT0);

        writel(BF_BCH_FLASH0LAYOUT1_PAGE_SIZE(page_size)
                        | BF_BCH_FLASH0LAYOUT1_ECCN(ecc_strength, this)
                        | BF_BCH_FLASH0LAYOUT1_GF(gf_len, this)
                        | BF_BCH_FLASH0LAYOUT1_DATAN_SIZE(block_size, this),
                        r->bch_regs + HW_BCH_FLASH0LAYOUT1);

        /* Set *all* chip selects to use layout 0. */
        writel(0, r->bch_regs + HW_BCH_LAYOUTSELECT);

        /* Enable interrupts. */
        writel(BM_BCH_CTRL_COMPLETE_IRQ_EN,
                                r->bch_regs + HW_BCH_CTRL_SET);

        gpmi_disable_clk(this);
        return 0;
err_out:
        gpmi_disable_clk(this);
        return ret;
}

/* Converts time in nanoseconds to cycles. */
static unsigned int ns_to_cycles(unsigned int time,
                        unsigned int period, unsigned int min)
{
        unsigned int k;

        k = (time + period - 1) / period;
        return max(k, min);
}

#define DEF_MIN_PROP_DELAY      5
#define DEF_MAX_PROP_DELAY      9
/* Apply timing to current hardware conditions. */
static int gpmi_nfc_compute_hardware_timing(struct gpmi_nand_data *this,
                                        struct gpmi_nfc_hardware_timing *hw)
{
        struct timing_threshold *nfc = &timing_default_threshold;
        struct resources *r = &this->resources;
        struct nand_chip *nand = &this->nand;
        struct nand_timing target = this->timing;
        bool improved_timing_is_available;
        unsigned long clock_frequency_in_hz;
        unsigned int clock_period_in_ns;
        bool dll_use_half_periods;
        unsigned int dll_delay_shift;
        unsigned int max_sample_delay_in_ns;
        unsigned int address_setup_in_cycles;
        unsigned int data_setup_in_ns;
        unsigned int data_setup_in_cycles;
        unsigned int data_hold_in_cycles;
        int ideal_sample_delay_in_ns;
        unsigned int sample_delay_factor;
        int tEYE;
        unsigned int min_prop_delay_in_ns = DEF_MIN_PROP_DELAY;
        unsigned int max_prop_delay_in_ns = DEF_MAX_PROP_DELAY;

        /*
         * If there are multiple chips, we need to relax the timings to allow
         * for signal distortion due to higher capacitance.
         */
        if (nand->numchips > 2) {
                target.data_setup_in_ns    += 10;
                target.data_hold_in_ns     += 10;
                target.address_setup_in_ns += 10;
        } else if (nand->numchips > 1) {
                target.data_setup_in_ns    += 5;
                target.data_hold_in_ns     += 5;
                target.address_setup_in_ns += 5;
        }

        /* Check if improved timing information is available. */
        improved_timing_is_available =
                (target.tREA_in_ns  >= 0) &&
                (target.tRLOH_in_ns >= 0) &&
                (target.tRHOH_in_ns >= 0);

        /* Inspect the clock. */
        nfc->clock_frequency_in_hz = clk_get_rate(r->clock[0]);
        clock_frequency_in_hz = nfc->clock_frequency_in_hz;
        clock_period_in_ns    = NSEC_PER_SEC / clock_frequency_in_hz;

        /*
         * The NFC quantizes setup and hold parameters in terms of clock cycles.
         * Here, we quantize the setup and hold timing parameters to the
         * next-highest clock period to make sure we apply at least the
         * specified times.
         *
         * For data setup and data hold, the hardware interprets a value of zero
         * as the largest possible delay. This is not what's intended by a zero
         * in the input parameter, so we impose a minimum of one cycle.
         */
        data_setup_in_cycles    = ns_to_cycles(target.data_setup_in_ns,
                                                        clock_period_in_ns, 1);
        data_hold_in_cycles     = ns_to_cycles(target.data_hold_in_ns,
                                                        clock_period_in_ns, 1);
        address_setup_in_cycles = ns_to_cycles(target.address_setup_in_ns,
                                                        clock_period_in_ns, 0);

        /*
         * The clock's period affects the sample delay in a number of ways:
         *
         * (1) The NFC HAL tells us the maximum clock period the sample delay
         *     DLL can tolerate. If the clock period is greater than half that
         *     maximum, we must configure the DLL to be driven by half periods.
         *
         * (2) We need to convert from an ideal sample delay, in ns, to a
         *     "sample delay factor," which the NFC uses. This factor depends on
         *     whether we're driving the DLL with full or half periods.
         *     Paraphrasing the reference manual:
         *
         *         AD = SDF x 0.125 x RP
         *
         * where:
         *
         *     AD   is the applied delay, in ns.
         *     SDF  is the sample delay factor, which is dimensionless.
         *     RP   is the reference period, in ns, which is a full clock period
         *          if the DLL is being driven by full periods, or half that if
         *          the DLL is being driven by half periods.
         *
         * Let's re-arrange this in a way that's more useful to us:
         *
         *                        8
         *         SDF  =  AD x ----
         *                       RP
         *
         * The reference period is either the clock period or half that, so this
         * is:
         *
         *                        8       AD x DDF
         *         SDF  =  AD x -----  =  --------
         *                      f x P        P
         *
         * where:
         *
         *       f  is 1 or 1/2, depending on how we're driving the DLL.
         *       P  is the clock period.
         *     DDF  is the DLL Delay Factor, a dimensionless value that
         *          incorporates all the constants in the conversion.
         *
         * DDF will be either 8 or 16, both of which are powers of two. We can
         * reduce the cost of this conversion by using bit shifts instead of
         * multiplication or division. Thus:
         *
         *                 AD << DDS
         *         SDF  =  ---------
         *                     P
         *
         *     or
         *
         *         AD  =  (SDF >> DDS) x P
         *
         * where:
         *
         *     DDS  is the DLL Delay Shift, the logarithm to base 2 of the DDF.
         */
        if (clock_period_in_ns > (nfc->max_dll_clock_period_in_ns >> 1)) {
                dll_use_half_periods = true;
                dll_delay_shift      = 3 + 1;
        } else {
                dll_use_half_periods = false;
                dll_delay_shift      = 3;
        }

        /*
         * Compute the maximum sample delay the NFC allows, under current
         * conditions. If the clock is running too slowly, no sample delay is
         * possible.
         */
        if (clock_period_in_ns > nfc->max_dll_clock_period_in_ns)
                max_sample_delay_in_ns = 0;
        else {
                /*
                 * Compute the delay implied by the largest sample delay factor
                 * the NFC allows.
                 */
                max_sample_delay_in_ns =
                        (nfc->max_sample_delay_factor * clock_period_in_ns) >>
                                                                dll_delay_shift;

                /*
                 * Check if the implied sample delay larger than the NFC
                 * actually allows.
                 */
                if (max_sample_delay_in_ns > nfc->max_dll_delay_in_ns)
                        max_sample_delay_in_ns = nfc->max_dll_delay_in_ns;
        }

        /*
         * Check if improved timing information is available. If not, we have to
         * use a less-sophisticated algorithm.
         */
        if (!improved_timing_is_available) {
                /*
                 * Fold the read setup time required by the NFC into the ideal
                 * sample delay.
                 */
                ideal_sample_delay_in_ns = target.gpmi_sample_delay_in_ns +
                                                nfc->internal_data_setup_in_ns;

                /*
                 * The ideal sample delay may be greater than the maximum
                 * allowed by the NFC. If so, we can trade off sample delay time
                 * for more data setup time.
                 *
                 * In each iteration of the following loop, we add a cycle to
                 * the data setup time and subtract a corresponding amount from
                 * the sample delay until we've satisified the constraints or
                 * can't do any better.
                 */
                while ((ideal_sample_delay_in_ns > max_sample_delay_in_ns) &&
                        (data_setup_in_cycles < nfc->max_data_setup_cycles)) {

                        data_setup_in_cycles++;
                        ideal_sample_delay_in_ns -= clock_period_in_ns;

                        if (ideal_sample_delay_in_ns < 0)
                                ideal_sample_delay_in_ns = 0;

                }

                /*
                 * Compute the sample delay factor that corresponds most closely
                 * to the ideal sample delay. If the result is too large for the
                 * NFC, use the maximum value.
                 *
                 * Notice that we use the ns_to_cycles function to compute the
                 * sample delay factor. We do this because the form of the
                 * computation is the same as that for calculating cycles.
                 */
                sample_delay_factor =
                        ns_to_cycles(
                                ideal_sample_delay_in_ns << dll_delay_shift,
                                                        clock_period_in_ns, 0);

                if (sample_delay_factor > nfc->max_sample_delay_factor)
                        sample_delay_factor = nfc->max_sample_delay_factor;

                /* Skip to the part where we return our results. */
                goto return_results;
        }

        /*
         * If control arrives here, we have more detailed timing information,
         * so we can use a better algorithm.
         */

        /*
         * Fold the read setup time required by the NFC into the maximum
         * propagation delay.
         */
        max_prop_delay_in_ns += nfc->internal_data_setup_in_ns;

        /*
         * Earlier, we computed the number of clock cycles required to satisfy
         * the data setup time. Now, we need to know the actual nanoseconds.
         */
        data_setup_in_ns = clock_period_in_ns * data_setup_in_cycles;

        /*
         * Compute tEYE, the width of the data eye when reading from the NAND
         * Flash. The eye width is fundamentally determined by the data setup
         * time, perturbed by propagation delays and some characteristics of the
         * NAND Flash device.
         *
         * start of the eye = max_prop_delay + tREA
         * end of the eye   = min_prop_delay + tRHOH + data_setup
         */
        tEYE = (int)min_prop_delay_in_ns + (int)target.tRHOH_in_ns +
                                                        (int)data_setup_in_ns;

        tEYE -= (int)max_prop_delay_in_ns + (int)target.tREA_in_ns;

        /*
         * The eye must be open. If it's not, we can try to open it by
         * increasing its main forcer, the data setup time.
         *
         * In each iteration of the following loop, we increase the data setup
         * time by a single clock cycle. We do this until either the eye is
         * open or we run into NFC limits.
         */
        while ((tEYE <= 0) &&
                        (data_setup_in_cycles < nfc->max_data_setup_cycles)) {
                /* Give a cycle to data setup. */
                data_setup_in_cycles++;
                /* Synchronize the data setup time with the cycles. */
                data_setup_in_ns += clock_period_in_ns;
                /* Adjust tEYE accordingly. */
                tEYE += clock_period_in_ns;
        }

        /*
         * When control arrives here, the eye is open. The ideal time to sample
         * the data is in the center of the eye:
         *
         *     end of the eye + start of the eye
         *     ---------------------------------  -  data_setup
         *                    2
         *
         * After some algebra, this simplifies to the code immediately below.
         */
        ideal_sample_delay_in_ns =
                ((int)max_prop_delay_in_ns +
                        (int)target.tREA_in_ns +
                                (int)min_prop_delay_in_ns +
                                        (int)target.tRHOH_in_ns -
                                                (int)data_setup_in_ns) >> 1;

        /*
         * The following figure illustrates some aspects of a NAND Flash read:
         *
         *
         *           __                   _____________________________________
         * RDN         \_________________/
         *
         *                                         <---- tEYE ----->
         *                                        /-----------------\
         * Read Data ----------------------------<                   >---------
         *                                        \-----------------/
         *             ^                 ^                 ^              ^
         *             |                 |                 |              |
         *             |<--Data Setup -->|<--Delay Time -->|              |
         *             |                 |                 |              |
         *             |                 |                                |
         *             |                 |<--   Quantized Delay Time   -->|
         *             |                 |                                |
         *
         *
         * We have some issues we must now address:
         *
         * (1) The *ideal* sample delay time must not be negative. If it is, we
         *     jam it to zero.
         *
         * (2) The *ideal* sample delay time must not be greater than that
         *     allowed by the NFC. If it is, we can increase the data setup
         *     time, which will reduce the delay between the end of the data
         *     setup and the center of the eye. It will also make the eye
         *     larger, which might help with the next issue...
         *
         * (3) The *quantized* sample delay time must not fall either before the
         *     eye opens or after it closes (the latter is the problem
         *     illustrated in the above figure).
         */

        /* Jam a negative ideal sample delay to zero. */
        if (ideal_sample_delay_in_ns < 0)
                ideal_sample_delay_in_ns = 0;

        /*
         * Extend the data setup as needed to reduce the ideal sample delay
         * below the maximum permitted by the NFC.
         */
        while ((ideal_sample_delay_in_ns > max_sample_delay_in_ns) &&
                        (data_setup_in_cycles < nfc->max_data_setup_cycles)) {

                /* Give a cycle to data setup. */
                data_setup_in_cycles++;
                /* Synchronize the data setup time with the cycles. */
                data_setup_in_ns += clock_period_in_ns;
                /* Adjust tEYE accordingly. */
                tEYE += clock_period_in_ns;

                /*
                 * Decrease the ideal sample delay by one half cycle, to keep it
                 * in the middle of the eye.
                 */
                ideal_sample_delay_in_ns -= (clock_period_in_ns >> 1);

                /* Jam a negative ideal sample delay to zero. */
                if (ideal_sample_delay_in_ns < 0)
                        ideal_sample_delay_in_ns = 0;
        }

        /*
         * Compute the sample delay factor that corresponds to the ideal sample
         * delay. If the result is too large, then use the maximum allowed
         * value.
         *
         * Notice that we use the ns_to_cycles function to compute the sample
         * delay factor. We do this because the form of the computation is the
         * same as that for calculating cycles.
         */
        sample_delay_factor =
                ns_to_cycles(ideal_sample_delay_in_ns << dll_delay_shift,
                                                        clock_period_in_ns, 0);

        if (sample_delay_factor > nfc->max_sample_delay_factor)
                sample_delay_factor = nfc->max_sample_delay_factor;

        /*
         * These macros conveniently encapsulate a computation we'll use to
         * continuously evaluate whether or not the data sample delay is inside
         * the eye.
         */
        #define IDEAL_DELAY  ((int) ideal_sample_delay_in_ns)

        #define QUANTIZED_DELAY  \
                ((int) ((sample_delay_factor * clock_period_in_ns) >> \
                                                        dll_delay_shift))

        #define DELAY_ERROR  (abs(QUANTIZED_DELAY - IDEAL_DELAY))

        #define SAMPLE_IS_NOT_WITHIN_THE_EYE  (DELAY_ERROR > (tEYE >> 1))

        /*
         * While the quantized sample time falls outside the eye, reduce the
         * sample delay or extend the data setup to move the sampling point back
         * toward the eye. Do not allow the number of data setup cycles to
         * exceed the maximum allowed by the NFC.
         */
        while (SAMPLE_IS_NOT_WITHIN_THE_EYE &&
                        (data_setup_in_cycles < nfc->max_data_setup_cycles)) {
                /*
                 * If control arrives here, the quantized sample delay falls
                 * outside the eye. Check if it's before the eye opens, or after
                 * the eye closes.
                 */
                if (QUANTIZED_DELAY > IDEAL_DELAY) {
                        /*
                         * If control arrives here, the quantized sample delay
                         * falls after the eye closes. Decrease the quantized
                         * delay time and then go back to re-evaluate.
                         */
                        if (sample_delay_factor != 0)
                                sample_delay_factor--;
                        continue;
                }

                /*
                 * If control arrives here, the quantized sample delay falls
                 * before the eye opens. Shift the sample point by increasing
                 * data setup time. This will also make the eye larger.
                 */

                /* Give a cycle to data setup. */
                data_setup_in_cycles++;
                /* Synchronize the data setup time with the cycles. */
                data_setup_in_ns += clock_period_in_ns;
                /* Adjust tEYE accordingly. */
                tEYE += clock_period_in_ns;

                /*
                 * Decrease the ideal sample delay by one half cycle, to keep it
                 * in the middle of the eye.
                 */
                ideal_sample_delay_in_ns -= (clock_period_in_ns >> 1);

                /* ...and one less period for the delay time. */
                ideal_sample_delay_in_ns -= clock_period_in_ns;

                /* Jam a negative ideal sample delay to zero. */
                if (ideal_sample_delay_in_ns < 0)
                        ideal_sample_delay_in_ns = 0;

                /*
                 * We have a new ideal sample delay, so re-compute the quantized
                 * delay.
                 */
                sample_delay_factor =
                        ns_to_cycles(
                                ideal_sample_delay_in_ns << dll_delay_shift,
                                                        clock_period_in_ns, 0);

                if (sample_delay_factor > nfc->max_sample_delay_factor)
                        sample_delay_factor = nfc->max_sample_delay_factor;
        }

        /* Control arrives here when we're ready to return our results. */
return_results:
        hw->data_setup_in_cycles    = data_setup_in_cycles;
        hw->data_hold_in_cycles     = data_hold_in_cycles;
        hw->address_setup_in_cycles = address_setup_in_cycles;
        hw->use_half_periods        = dll_use_half_periods;
        hw->sample_delay_factor     = sample_delay_factor;
        hw->device_busy_timeout     = GPMI_DEFAULT_BUSY_TIMEOUT;
        hw->wrn_dly_sel             = BV_GPMI_CTRL1_WRN_DLY_SEL_4_TO_8NS;

        /* Return success. */
        return 0;
}

/*
 * <1> Firstly, we should know what's the GPMI-clock means.
 *     The GPMI-clock is the internal clock in the gpmi nand controller.
 *     If you set 100MHz to gpmi nand controller, the GPMI-clock's period
 *     is 10ns. Mark the GPMI-clock's period as GPMI-clock-period.
 *
 * <2> Secondly, we should know what's the frequency on the nand chip pins.
 *     The frequency on the nand chip pins is derived from the GPMI-clock.
 *     We can get it from the following equation:
 *
 *         F = G / (DS + DH)
 *
 *         F  : the frequency on the nand chip pins.
 *         G  : the GPMI clock, such as 100MHz.
 *         DS : GPMI_HW_GPMI_TIMING0:DATA_SETUP
 *         DH : GPMI_HW_GPMI_TIMING0:DATA_HOLD
 *
 * <3> Thirdly, when the frequency on the nand chip pins is above 33MHz,
 *     the nand EDO(extended Data Out) timing could be applied.
 *     The GPMI implements a feedback read strobe to sample the read data.
 *     The feedback read strobe can be delayed to support the nand EDO timing
 *     where the read strobe may deasserts before the read data is valid, and
 *     read data is valid for some time after read strobe.
 *
 *     The following figure illustrates some aspects of a NAND Flash read:
 *
 *                   |<---tREA---->|
 *                   |             |
 *                   |         |   |
 *                   |<--tRP-->|   |
 *                   |         |   |
 *                  __          ___|__________________________________
 *     RDN            \________/   |
 *                                 |
 *                                 /---------\
 *     Read Data    --------------<           >---------
 *                                 \---------/
 *                                |     |
 *                                |<-D->|
 *     FeedbackRDN  ________             ____________
 *                          \___________/
 *
 *          D stands for delay, set in the HW_GPMI_CTRL1:RDN_DELAY.
 *
 *
 * <4> Now, we begin to describe how to compute the right RDN_DELAY.
 *
 *  4.1) From the aspect of the nand chip pins:
 *        Delay = (tREA + C - tRP)               {1}
 *
 *        tREA : the maximum read access time. From the ONFI nand standards,
 *               we know that tREA is 16ns in mode 5, tREA is 20ns is mode 4.
 *               Please check it in : www.onfi.org
 *        C    : a constant for adjust the delay. default is 4.
 *        tRP  : the read pulse width.
 *               Specified by the HW_GPMI_TIMING0:DATA_SETUP:
 *                    tRP = (GPMI-clock-period) * DATA_SETUP
 *
 *  4.2) From the aspect of the GPMI nand controller:
 *         Delay = RDN_DELAY * 0.125 * RP        {2}
 *
 *         RP   : the DLL reference period.
 *            if (GPMI-clock-period > DLL_THRETHOLD)
 *                   RP = GPMI-clock-period / 2;
 *            else
 *                   RP = GPMI-clock-period;
 *
 *            Set the HW_GPMI_CTRL1:HALF_PERIOD if GPMI-clock-period
 *            is greater DLL_THRETHOLD. In other SOCs, the DLL_THRETHOLD
 *            is 16ns, but in mx6q, we use 12ns.
 *
 *  4.3) since {1} equals {2}, we get:
 *
 *                    (tREA + 4 - tRP) * 8
 *         RDN_DELAY = ---------------------     {3}
 *                           RP
 *
 *  4.4) We only support the fastest asynchronous mode of ONFI nand.
 *       For some ONFI nand, the mode 4 is the fastest mode;
 *       while for some ONFI nand, the mode 5 is the fastest mode.
 *       So we only support the mode 4 and mode 5. It is no need to
 *       support other modes.
 */
static void gpmi_compute_edo_timing(struct gpmi_nand_data *this,
                        struct gpmi_nfc_hardware_timing *hw)
{
        struct resources *r = &this->resources;
        unsigned long rate = clk_get_rate(r->clock[0]);
        int mode = this->timing_mode;
        int dll_threshold = this->devdata->max_chain_delay;
        unsigned long delay;
        unsigned long clk_period;
        int t_rea;
        int c = 4;
        int t_rp;
        int rp;

        /*
         * [1] for GPMI_HW_GPMI_TIMING0:
         *     The async mode requires 40MHz for mode 4, 50MHz for mode 5.
         *     The GPMI can support 100MHz at most. So if we want to
         *     get the 40MHz or 50MHz, we have to set DS=1, DH=1.
         *     Set the ADDRESS_SETUP to 0 in mode 4.
         */
        hw->data_setup_in_cycles = 1;
        hw->data_hold_in_cycles = 1;
        hw->address_setup_in_cycles = ((mode == 5) ? 1 : 0);

        /* [2] for GPMI_HW_GPMI_TIMING1 */
        hw->device_busy_timeout = 0x9000;

        /* [3] for GPMI_HW_GPMI_CTRL1 */
        hw->wrn_dly_sel = BV_GPMI_CTRL1_WRN_DLY_SEL_NO_DELAY;

        /*
         * Enlarge 10 times for the numerator and denominator in {3}.
         * This make us to get more accurate result.
         */
        clk_period = NSEC_PER_SEC / (rate / 10);
        dll_threshold *= 10;
        t_rea = ((mode == 5) ? 16 : 20) * 10;
        c *= 10;

        t_rp = clk_period * 1; /* DATA_SETUP is 1 */

        if (clk_period > dll_threshold) {
                hw->use_half_periods = 1;
                rp = clk_period / 2;
        } else {
                hw->use_half_periods = 0;
                rp = clk_period;
        }

        /*
         * Multiply the numerator with 10, we could do a round off:
         *      7.8 round up to 8; 7.4 round down to 7.
         */
        delay  = (((t_rea + c - t_rp) * 8) * 10) / rp;
        delay = (delay + 5) / 10;

        hw->sample_delay_factor = delay;
}

static int enable_edo_mode(struct gpmi_nand_data *this, int mode)
{
        struct resources  *r = &this->resources;
        struct nand_chip *nand = &this->nand;
        struct mtd_info  *mtd = nand_to_mtd(nand);
        uint8_t *feature;
        unsigned long rate;
        int ret;

        feature = kzalloc(ONFI_SUBFEATURE_PARAM_LEN, GFP_KERNEL);
        if (!feature)
                return -ENOMEM;

        nand->select_chip(mtd, 0);

        /* [1] send SET FEATURE command to NAND */
        feature[0] = mode;
        ret = nand->onfi_set_features(mtd, nand,
                                ONFI_FEATURE_ADDR_TIMING_MODE, feature);
        if (ret)
                goto err_out;

        /* [2] send GET FEATURE command to double-check the timing mode */
        memset(feature, 0, ONFI_SUBFEATURE_PARAM_LEN);
        ret = nand->onfi_get_features(mtd, nand,
                                ONFI_FEATURE_ADDR_TIMING_MODE, feature);
        if (ret || feature[0] != mode)
                goto err_out;

        nand->select_chip(mtd, -1);

        /* [3] set the main IO clock, 100MHz for mode 5, 80MHz for mode 4. */
        rate = (mode == 5) ? 100000000 : 80000000;
        clk_set_rate(r->clock[0], rate);

        /* Let the gpmi_begin() re-compute the timing again. */
        this->flags &= ~GPMI_TIMING_INIT_OK;

        this->flags |= GPMI_ASYNC_EDO_ENABLED;
        this->timing_mode = mode;
        kfree(feature);
        dev_info(this->dev, "enable the asynchronous EDO mode %d\n", mode);
        return 0;

err_out:
        nand->select_chip(mtd, -1);
        kfree(feature);
        dev_err(this->dev, "mode:%d ,failed in set feature.\n", mode);
        return -EINVAL;
}

int gpmi_extra_init(struct gpmi_nand_data *this)
{
        struct nand_chip *chip = &this->nand;

        /* Enable the asynchronous EDO feature. */
        if (GPMI_IS_MX6(this) && chip->onfi_version) {
                int mode = onfi_get_async_timing_mode(chip);

                /* We only support the timing mode 4 and mode 5. */
                if (mode & ONFI_TIMING_MODE_5)
                        mode = 5;
                else if (mode & ONFI_TIMING_MODE_4)
                        mode = 4;
                else
                        return 0;

                return enable_edo_mode(this, mode);
        }
        return 0;
}

/* Begin the I/O */
void gpmi_begin(struct gpmi_nand_data *this)
{
        struct resources *r = &this->resources;
        void __iomem *gpmi_regs = r->gpmi_regs;
        unsigned int   clock_period_in_ns;
        uint32_t       reg;
        unsigned int   dll_wait_time_in_us;
        struct gpmi_nfc_hardware_timing  hw;

        int ret;

        /* Enable the clock. */
        ret = gpmi_enable_clk(this);
        if (ret) {
                dev_err(this->dev, "We failed in enable the clk\n");
                goto err_out;
        }

        /* Only initialize the timing once */
        if (this->flags & GPMI_TIMING_INIT_OK)
                return;
        this->flags |= GPMI_TIMING_INIT_OK;

        if (this->flags & GPMI_ASYNC_EDO_ENABLED)
                gpmi_compute_edo_timing(this, &hw);
        else
                gpmi_nfc_compute_hardware_timing(this, &hw);

        /* [1] Set HW_GPMI_TIMING0 */
        reg = BF_GPMI_TIMING0_ADDRESS_SETUP(hw.address_setup_in_cycles) |
                BF_GPMI_TIMING0_DATA_HOLD(hw.data_hold_in_cycles)         |
                BF_GPMI_TIMING0_DATA_SETUP(hw.data_setup_in_cycles);

        writel(reg, gpmi_regs + HW_GPMI_TIMING0);

        /* [2] Set HW_GPMI_TIMING1 */
        writel(BF_GPMI_TIMING1_BUSY_TIMEOUT(hw.device_busy_timeout),
                gpmi_regs + HW_GPMI_TIMING1);

        /* [3] The following code is to set the HW_GPMI_CTRL1. */

        /* Set the WRN_DLY_SEL */
        writel(BM_GPMI_CTRL1_WRN_DLY_SEL, gpmi_regs + HW_GPMI_CTRL1_CLR);
        writel(BF_GPMI_CTRL1_WRN_DLY_SEL(hw.wrn_dly_sel),
                                        gpmi_regs + HW_GPMI_CTRL1_SET);

        /* DLL_ENABLE must be set to 0 when setting RDN_DELAY or HALF_PERIOD. */
        writel(BM_GPMI_CTRL1_DLL_ENABLE, gpmi_regs + HW_GPMI_CTRL1_CLR);

        /* Clear out the DLL control fields. */
        reg = BM_GPMI_CTRL1_RDN_DELAY | BM_GPMI_CTRL1_HALF_PERIOD;
        writel(reg, gpmi_regs + HW_GPMI_CTRL1_CLR);

        /* If no sample delay is called for, return immediately. */
        if (!hw.sample_delay_factor)
                return;

        /* Set RDN_DELAY or HALF_PERIOD. */
        reg = ((hw.use_half_periods) ? BM_GPMI_CTRL1_HALF_PERIOD : 0)
                | BF_GPMI_CTRL1_RDN_DELAY(hw.sample_delay_factor);

        writel(reg, gpmi_regs + HW_GPMI_CTRL1_SET);

        /* At last, we enable the DLL. */
        writel(BM_GPMI_CTRL1_DLL_ENABLE, gpmi_regs + HW_GPMI_CTRL1_SET);

        /*
         * After we enable the GPMI DLL, we have to wait 64 clock cycles before
         * we can use the GPMI. Calculate the amount of time we need to wait,
         * in microseconds.
         */
        clock_period_in_ns = NSEC_PER_SEC / clk_get_rate(r->clock[0]);
        dll_wait_time_in_us = (clock_period_in_ns * 64) / 1000;

        if (!dll_wait_time_in_us)
                dll_wait_time_in_us = 1;

        /* Wait for the DLL to settle. */
        udelay(dll_wait_time_in_us);

err_out:
        return;
}

void gpmi_end(struct gpmi_nand_data *this)
{
        gpmi_disable_clk(this);
}

/* Clears a BCH interrupt. */
void gpmi_clear_bch(struct gpmi_nand_data *this)
{
        struct resources *r = &this->resources;
        writel(BM_BCH_CTRL_COMPLETE_IRQ, r->bch_regs + HW_BCH_CTRL_CLR);
}

/* Returns the Ready/Busy status of the given chip. */
int gpmi_is_ready(struct gpmi_nand_data *this, unsigned chip)
{
        struct resources *r = &this->resources;
        uint32_t mask = 0;
        uint32_t reg = 0;

        if (GPMI_IS_MX23(this)) {
                mask = MX23_BM_GPMI_DEBUG_READY0 << chip;
                reg = readl(r->gpmi_regs + HW_GPMI_DEBUG);
        } else if (GPMI_IS_MX28(this) || GPMI_IS_MX6(this)) {
                /*
                 * In the imx6, all the ready/busy pins are bound
                 * together. So we only need to check chip 0.
                 */
                if (GPMI_IS_MX6(this))
                        chip = 0;

                /* MX28 shares the same R/B register as MX6Q. */
                mask = MX28_BF_GPMI_STAT_READY_BUSY(1 << chip);
                reg = readl(r->gpmi_regs + HW_GPMI_STAT);
        } else
                dev_err(this->dev, "unknown arch.\n");
        return reg & mask;
}

static inline void set_dma_type(struct gpmi_nand_data *this,
                                        enum dma_ops_type type)
{
        this->last_dma_type = this->dma_type;
        this->dma_type = type;
}

int gpmi_send_command(struct gpmi_nand_data *this)
{
        struct dma_chan *channel = get_dma_chan(this);
        struct dma_async_tx_descriptor *desc;
        struct scatterlist *sgl;
        int chip = this->current_chip;
        u32 pio[3];

        /* [1] send out the PIO words */
        pio[0] = BF_GPMI_CTRL0_COMMAND_MODE(BV_GPMI_CTRL0_COMMAND_MODE__WRITE)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(BV_GPMI_CTRL0_ADDRESS__NAND_CLE)
                | BM_GPMI_CTRL0_ADDRESS_INCREMENT
                | BF_GPMI_CTRL0_XFER_COUNT(this->command_length);
        pio[1] = pio[2] = 0;
        desc = dmaengine_prep_slave_sg(channel,
                                        (struct scatterlist *)pio,
                                        ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
        if (!desc)
                return -EINVAL;

        /* [2] send out the COMMAND + ADDRESS string stored in @buffer */
        sgl = &this->cmd_sgl;

        sg_init_one(sgl, this->cmd_buffer, this->command_length);
        dma_map_sg(this->dev, sgl, 1, DMA_TO_DEVICE);
        desc = dmaengine_prep_slave_sg(channel,
                                sgl, 1, DMA_MEM_TO_DEV,
                                DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        /* [3] submit the DMA */
        set_dma_type(this, DMA_FOR_COMMAND);
        return start_dma_without_bch_irq(this, desc);
}

int gpmi_send_data(struct gpmi_nand_data *this)
{
        struct dma_async_tx_descriptor *desc;
        struct dma_chan *channel = get_dma_chan(this);
        int chip = this->current_chip;
        uint32_t command_mode;
        uint32_t address;
        u32 pio[2];

        /* [1] PIO */
        command_mode = BV_GPMI_CTRL0_COMMAND_MODE__WRITE;
        address      = BV_GPMI_CTRL0_ADDRESS__NAND_DATA;

        pio[0] = BF_GPMI_CTRL0_COMMAND_MODE(command_mode)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(address)
                | BF_GPMI_CTRL0_XFER_COUNT(this->upper_len);
        pio[1] = 0;
        desc = dmaengine_prep_slave_sg(channel, (struct scatterlist *)pio,
                                        ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
        if (!desc)
                return -EINVAL;

        /* [2] send DMA request */
        prepare_data_dma(this, DMA_TO_DEVICE);
        desc = dmaengine_prep_slave_sg(channel, &this->data_sgl,
                                        1, DMA_MEM_TO_DEV,
                                        DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        /* [3] submit the DMA */
        set_dma_type(this, DMA_FOR_WRITE_DATA);
        return start_dma_without_bch_irq(this, desc);
}

int gpmi_read_data(struct gpmi_nand_data *this)
{
        struct dma_async_tx_descriptor *desc;
        struct dma_chan *channel = get_dma_chan(this);
        int chip = this->current_chip;
        u32 pio[2];

        /* [1] : send PIO */
        pio[0] = BF_GPMI_CTRL0_COMMAND_MODE(BV_GPMI_CTRL0_COMMAND_MODE__READ)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(BV_GPMI_CTRL0_ADDRESS__NAND_DATA)
                | BF_GPMI_CTRL0_XFER_COUNT(this->upper_len);
        pio[1] = 0;
        desc = dmaengine_prep_slave_sg(channel,
                                        (struct scatterlist *)pio,
                                        ARRAY_SIZE(pio), DMA_TRANS_NONE, 0);
        if (!desc)
                return -EINVAL;

        /* [2] : send DMA request */
        prepare_data_dma(this, DMA_FROM_DEVICE);
        desc = dmaengine_prep_slave_sg(channel, &this->data_sgl,
                                        1, DMA_DEV_TO_MEM,
                                        DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        /* [3] : submit the DMA */
        set_dma_type(this, DMA_FOR_READ_DATA);
        return start_dma_without_bch_irq(this, desc);
}

int gpmi_send_page(struct gpmi_nand_data *this,
                        dma_addr_t payload, dma_addr_t auxiliary)
{
        struct bch_geometry *geo = &this->bch_geometry;
        uint32_t command_mode;
        uint32_t address;
        uint32_t ecc_command;
        uint32_t buffer_mask;
        struct dma_async_tx_descriptor *desc;
        struct dma_chan *channel = get_dma_chan(this);
        int chip = this->current_chip;
        u32 pio[6];

        /* A DMA descriptor that does an ECC page read. */
        command_mode = BV_GPMI_CTRL0_COMMAND_MODE__WRITE;
        address      = BV_GPMI_CTRL0_ADDRESS__NAND_DATA;
        ecc_command  = BV_GPMI_ECCCTRL_ECC_CMD__BCH_ENCODE;
        buffer_mask  = BV_GPMI_ECCCTRL_BUFFER_MASK__BCH_PAGE |
                                BV_GPMI_ECCCTRL_BUFFER_MASK__BCH_AUXONLY;

        pio[0] = BF_GPMI_CTRL0_COMMAND_MODE(command_mode)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(address)
                | BF_GPMI_CTRL0_XFER_COUNT(0);
        pio[1] = 0;
        pio[2] = BM_GPMI_ECCCTRL_ENABLE_ECC
                | BF_GPMI_ECCCTRL_ECC_CMD(ecc_command)
                | BF_GPMI_ECCCTRL_BUFFER_MASK(buffer_mask);
        pio[3] = geo->page_size;
        pio[4] = payload;
        pio[5] = auxiliary;

        desc = dmaengine_prep_slave_sg(channel,
                                        (struct scatterlist *)pio,
                                        ARRAY_SIZE(pio), DMA_TRANS_NONE,
                                        DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        set_dma_type(this, DMA_FOR_WRITE_ECC_PAGE);
        return start_dma_with_bch_irq(this, desc);
}

int gpmi_read_page(struct gpmi_nand_data *this,
                                dma_addr_t payload, dma_addr_t auxiliary)
{
        struct bch_geometry *geo = &this->bch_geometry;
        uint32_t command_mode;
        uint32_t address;
        uint32_t ecc_command;
        uint32_t buffer_mask;
        struct dma_async_tx_descriptor *desc;
        struct dma_chan *channel = get_dma_chan(this);
        int chip = this->current_chip;
        u32 pio[6];

        /* [1] Wait for the chip to report ready. */
        command_mode = BV_GPMI_CTRL0_COMMAND_MODE__WAIT_FOR_READY;
        address      = BV_GPMI_CTRL0_ADDRESS__NAND_DATA;

        pio[0] =  BF_GPMI_CTRL0_COMMAND_MODE(command_mode)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(address)
                | BF_GPMI_CTRL0_XFER_COUNT(0);
        pio[1] = 0;
        desc = dmaengine_prep_slave_sg(channel,
                                (struct scatterlist *)pio, 2,
                                DMA_TRANS_NONE, 0);
        if (!desc)
                return -EINVAL;

        /* [2] Enable the BCH block and read. */
        command_mode = BV_GPMI_CTRL0_COMMAND_MODE__READ;
        address      = BV_GPMI_CTRL0_ADDRESS__NAND_DATA;
        ecc_command  = BV_GPMI_ECCCTRL_ECC_CMD__BCH_DECODE;
        buffer_mask  = BV_GPMI_ECCCTRL_BUFFER_MASK__BCH_PAGE
                        | BV_GPMI_ECCCTRL_BUFFER_MASK__BCH_AUXONLY;

        pio[0] =  BF_GPMI_CTRL0_COMMAND_MODE(command_mode)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(address)
                | BF_GPMI_CTRL0_XFER_COUNT(geo->page_size);

        pio[1] = 0;
        pio[2] =  BM_GPMI_ECCCTRL_ENABLE_ECC
                | BF_GPMI_ECCCTRL_ECC_CMD(ecc_command)
                | BF_GPMI_ECCCTRL_BUFFER_MASK(buffer_mask);
        pio[3] = geo->page_size;
        pio[4] = payload;
        pio[5] = auxiliary;
        desc = dmaengine_prep_slave_sg(channel,
                                        (struct scatterlist *)pio,
                                        ARRAY_SIZE(pio), DMA_TRANS_NONE,
                                        DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        /* [3] Disable the BCH block */
        command_mode = BV_GPMI_CTRL0_COMMAND_MODE__WAIT_FOR_READY;
        address      = BV_GPMI_CTRL0_ADDRESS__NAND_DATA;

        pio[0] = BF_GPMI_CTRL0_COMMAND_MODE(command_mode)
                | BM_GPMI_CTRL0_WORD_LENGTH
                | BF_GPMI_CTRL0_CS(chip, this)
                | BF_GPMI_CTRL0_LOCK_CS(LOCK_CS_ENABLE, this)
                | BF_GPMI_CTRL0_ADDRESS(address)
                | BF_GPMI_CTRL0_XFER_COUNT(geo->page_size);
        pio[1] = 0;
        pio[2] = 0; /* clear GPMI_HW_GPMI_ECCCTRL, disable the BCH. */
        desc = dmaengine_prep_slave_sg(channel,
                                (struct scatterlist *)pio, 3,
                                DMA_TRANS_NONE,
                                DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
        if (!desc)
                return -EINVAL;

        /* [4] submit the DMA */
        set_dma_type(this, DMA_FOR_READ_ECC_PAGE);
        return start_dma_with_bch_irq(this, desc);
}

/**
 * gpmi_copy_bits - copy bits from one memory region to another
 * @dst: destination buffer
 * @dst_bit_off: bit offset we're starting to write at
 * @src: source buffer
 * @src_bit_off: bit offset we're starting to read from
 * @nbits: number of bits to copy
 *
 * This functions copies bits from one memory region to another, and is used by
 * the GPMI driver to copy ECC sections which are not guaranteed to be byte
 * aligned.
 *
 * src and dst should not overlap.
 *
 */
void gpmi_copy_bits(u8 *dst, size_t dst_bit_off,
                    const u8 *src, size_t src_bit_off,
                    size_t nbits)
{
        size_t i;
        size_t nbytes;
        u32 src_buffer = 0;
        size_t bits_in_src_buffer = 0;

        if (!nbits)
                return;

        /*
         * Move src and dst pointers to the closest byte pointer and store bit
         * offsets within a byte.
         */
        src += src_bit_off / 8;
        src_bit_off %= 8;

        dst += dst_bit_off / 8;
        dst_bit_off %= 8;

        /*
         * Initialize the src_buffer value with bits available in the first
         * byte of data so that we end up with a byte aligned src pointer.
         */
        if (src_bit_off) {
                src_buffer = src[0] >> src_bit_off;
                if (nbits >= (8 - src_bit_off)) {
                        bits_in_src_buffer += 8 - src_bit_off;
                } else {
                        src_buffer &= GENMASK(nbits - 1, 0);
                        bits_in_src_buffer += nbits;
                }
                nbits -= bits_in_src_buffer;
                src++;
        }

        /* Calculate the number of bytes that can be copied from src to dst. */
        nbytes = nbits / 8;

        /* Try to align dst to a byte boundary. */
        if (dst_bit_off) {
                if (bits_in_src_buffer < (8 - dst_bit_off) && nbytes) {
                        src_buffer |= src[0] << bits_in_src_buffer;
                        bits_in_src_buffer += 8;
                        src++;
                        nbytes--;
                }

                if (bits_in_src_buffer >= (8 - dst_bit_off)) {
                        dst[0] &= GENMASK(dst_bit_off - 1, 0);
                        dst[0] |= src_buffer << dst_bit_off;
                        src_buffer >>= (8 - dst_bit_off);
                        bits_in_src_buffer -= (8 - dst_bit_off);
                        dst_bit_off = 0;
                        dst++;
                        if (bits_in_src_buffer > 7) {
                                bits_in_src_buffer -= 8;
                                dst[0] = src_buffer;
                                dst++;
                                src_buffer >>= 8;
                        }
                }
        }

        if (!bits_in_src_buffer && !dst_bit_off) {
                /*
                 * Both src and dst pointers are byte aligned, thus we can
                 * just use the optimized memcpy function.
                 */
                if (nbytes)
                        memcpy(dst, src, nbytes);
        } else {
                /*
                 * src buffer is not byte aligned, hence we have to copy each
                 * src byte to the src_buffer variable before extracting a byte
                 * to store in dst.
                 */
                for (i = 0; i < nbytes; i++) {
                        src_buffer |= src[i] << bits_in_src_buffer;
                        dst[i] = src_buffer;
                        src_buffer >>= 8;
                }
        }
        /* Update dst and src pointers */
        dst += nbytes;
        src += nbytes;

        /*
         * nbits is the number of remaining bits. It should not exceed 8 as
         * we've already copied as much bytes as possible.
         */
        nbits %= 8;

        /*
         * If there's no more bits to copy to the destination and src buffer
         * was already byte aligned, then we're done.
         */
        if (!nbits && !bits_in_src_buffer)
                return;

        /* Copy the remaining bits to src_buffer */
        if (nbits)
                src_buffer |= (*src & GENMASK(nbits - 1, 0)) <<
                              bits_in_src_buffer;
        bits_in_src_buffer += nbits;

        /*
         * In case there were not enough bits to get a byte aligned dst buffer
         * prepare the src_buffer variable to match the dst organization (shift
         * src_buffer by dst_bit_off and retrieve the least significant bits
         * from dst).
         */
        if (dst_bit_off)
                src_buffer = (src_buffer << dst_bit_off) |
                             (*dst & GENMASK(dst_bit_off - 1, 0));
        bits_in_src_buffer += dst_bit_off;

        /*
         * Keep most significant bits from dst if we end up with an unaligned
         * number of bits.
         */
        nbytes = bits_in_src_buffer / 8;
        if (bits_in_src_buffer % 8) {
                src_buffer |= (dst[nbytes] &
                               GENMASK(7, bits_in_src_buffer % 8)) <<
                              (nbytes * 8);
                nbytes++;
        }

        /* Copy the remaining bytes to dst */
        for (i = 0; i < nbytes; i++) {
                dst[i] = src_buffer;
                src_buffer >>= 8;
        }
}