/*
 * Copyright (c) 2006 Dave Airlie <airlied@linux.ie>
 * Copyright © 2006-2008,2010 Intel Corporation
 *   Jesse Barnes <jesse.barnes@intel.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 *
 * Authors:
 *      Eric Anholt <eric@anholt.net>
 *      Chris Wilson <chris@chris-wilson.co.uk>
 */

#include <linux/export.h>
#include <linux/i2c-algo-bit.h>
#include <linux/i2c.h>

#include <drm/drm_hdcp.h>
#include <drm/i915_drm.h>

#include "i915_drv.h"
#include "intel_drv.h"
#include "intel_gmbus.h"

struct gmbus_pin {
        const char *name;
        enum i915_gpio gpio;
};

/* Map gmbus pin pairs to names and registers. */
static const struct gmbus_pin gmbus_pins[] = {
        [GMBUS_PIN_SSC] = { "ssc", GPIOB },
        [GMBUS_PIN_VGADDC] = { "vga", GPIOA },
        [GMBUS_PIN_PANEL] = { "panel", GPIOC },
        [GMBUS_PIN_DPC] = { "dpc", GPIOD },
        [GMBUS_PIN_DPB] = { "dpb", GPIOE },
        [GMBUS_PIN_DPD] = { "dpd", GPIOF },
};

static const struct gmbus_pin gmbus_pins_bdw[] = {
        [GMBUS_PIN_VGADDC] = { "vga", GPIOA },
        [GMBUS_PIN_DPC] = { "dpc", GPIOD },
        [GMBUS_PIN_DPB] = { "dpb", GPIOE },
        [GMBUS_PIN_DPD] = { "dpd", GPIOF },
};

static const struct gmbus_pin gmbus_pins_skl[] = {
        [GMBUS_PIN_DPC] = { "dpc", GPIOD },
        [GMBUS_PIN_DPB] = { "dpb", GPIOE },
        [GMBUS_PIN_DPD] = { "dpd", GPIOF },
};

static const struct gmbus_pin gmbus_pins_bxt[] = {
        [GMBUS_PIN_1_BXT] = { "dpb", GPIOB },
        [GMBUS_PIN_2_BXT] = { "dpc", GPIOC },
        [GMBUS_PIN_3_BXT] = { "misc", GPIOD },
};

static const struct gmbus_pin gmbus_pins_cnp[] = {
        [GMBUS_PIN_1_BXT] = { "dpb", GPIOB },
        [GMBUS_PIN_2_BXT] = { "dpc", GPIOC },
        [GMBUS_PIN_3_BXT] = { "misc", GPIOD },
        [GMBUS_PIN_4_CNP] = { "dpd", GPIOE },
};

static const struct gmbus_pin gmbus_pins_icp[] = {
        [GMBUS_PIN_1_BXT] = { "dpa", GPIOB },
        [GMBUS_PIN_2_BXT] = { "dpb", GPIOC },
        [GMBUS_PIN_9_TC1_ICP] = { "tc1", GPIOJ },
        [GMBUS_PIN_10_TC2_ICP] = { "tc2", GPIOK },
        [GMBUS_PIN_11_TC3_ICP] = { "tc3", GPIOL },
        [GMBUS_PIN_12_TC4_ICP] = { "tc4", GPIOM },
};

static const struct gmbus_pin gmbus_pins_mcc[] = {
        [GMBUS_PIN_1_BXT] = { "dpa", GPIOB },
        [GMBUS_PIN_2_BXT] = { "dpb", GPIOC },
        [GMBUS_PIN_9_TC1_ICP] = { "dpc", GPIOJ },
};

/* pin is expected to be valid */
static const struct gmbus_pin *get_gmbus_pin(struct drm_i915_private *dev_priv,
                                             unsigned int pin)
{
        if (HAS_PCH_MCC(dev_priv))
                return &gmbus_pins_mcc[pin];
        else if (HAS_PCH_ICP(dev_priv))
                return &gmbus_pins_icp[pin];
        else if (HAS_PCH_CNP(dev_priv))
                return &gmbus_pins_cnp[pin];
        else if (IS_GEN9_LP(dev_priv))
                return &gmbus_pins_bxt[pin];
        else if (IS_GEN9_BC(dev_priv))
                return &gmbus_pins_skl[pin];
        else if (IS_BROADWELL(dev_priv))
                return &gmbus_pins_bdw[pin];
        else
                return &gmbus_pins[pin];
}

bool intel_gmbus_is_valid_pin(struct drm_i915_private *dev_priv,
                              unsigned int pin)
{
        unsigned int size;

        if (HAS_PCH_MCC(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_mcc);
        else if (HAS_PCH_ICP(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_icp);
        else if (HAS_PCH_CNP(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_cnp);
        else if (IS_GEN9_LP(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_bxt);
        else if (IS_GEN9_BC(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_skl);
        else if (IS_BROADWELL(dev_priv))
                size = ARRAY_SIZE(gmbus_pins_bdw);
        else
                size = ARRAY_SIZE(gmbus_pins);

        return pin < size && get_gmbus_pin(dev_priv, pin)->name;
}

/* Intel GPIO access functions */

#define I2C_RISEFALL_TIME 10

static inline struct intel_gmbus *
to_intel_gmbus(struct i2c_adapter *i2c)
{
        return container_of(i2c, struct intel_gmbus, adapter);
}

void
intel_gmbus_reset(struct drm_i915_private *dev_priv)
{
        I915_WRITE(GMBUS0, 0);
        I915_WRITE(GMBUS4, 0);
}

static void pnv_gmbus_clock_gating(struct drm_i915_private *dev_priv,
                                   bool enable)
{
        u32 val;

        /* When using bit bashing for I2C, this bit needs to be set to 1 */
        val = I915_READ(DSPCLK_GATE_D);
        if (!enable)
                val |= PNV_GMBUSUNIT_CLOCK_GATE_DISABLE;
        else
                val &= ~PNV_GMBUSUNIT_CLOCK_GATE_DISABLE;
        I915_WRITE(DSPCLK_GATE_D, val);
}

static void pch_gmbus_clock_gating(struct drm_i915_private *dev_priv,
                                   bool enable)
{
        u32 val;

        val = I915_READ(SOUTH_DSPCLK_GATE_D);
        if (!enable)
                val |= PCH_GMBUSUNIT_CLOCK_GATE_DISABLE;
        else
                val &= ~PCH_GMBUSUNIT_CLOCK_GATE_DISABLE;
        I915_WRITE(SOUTH_DSPCLK_GATE_D, val);
}

static void bxt_gmbus_clock_gating(struct drm_i915_private *dev_priv,
                                   bool enable)
{
        u32 val;

        val = I915_READ(GEN9_CLKGATE_DIS_4);
        if (!enable)
                val |= BXT_GMBUS_GATING_DIS;
        else
                val &= ~BXT_GMBUS_GATING_DIS;
        I915_WRITE(GEN9_CLKGATE_DIS_4, val);
}

static u32 get_reserved(struct intel_gmbus *bus)
{
        struct drm_i915_private *i915 = bus->dev_priv;
        struct intel_uncore *uncore = &i915->uncore;
        u32 reserved = 0;

        /* On most chips, these bits must be preserved in software. */
        if (!IS_I830(i915) && !IS_I845G(i915))
                reserved = intel_uncore_read_notrace(uncore, bus->gpio_reg) &
                           (GPIO_DATA_PULLUP_DISABLE |
                            GPIO_CLOCK_PULLUP_DISABLE);

        return reserved;
}

static int get_clock(void *data)
{
        struct intel_gmbus *bus = data;
        struct intel_uncore *uncore = &bus->dev_priv->uncore;
        u32 reserved = get_reserved(bus);

        intel_uncore_write_notrace(uncore,
                                   bus->gpio_reg,
                                   reserved | GPIO_CLOCK_DIR_MASK);
        intel_uncore_write_notrace(uncore, bus->gpio_reg, reserved);

        return (intel_uncore_read_notrace(uncore, bus->gpio_reg) &
                GPIO_CLOCK_VAL_IN) != 0;
}

static int get_data(void *data)
{
        struct intel_gmbus *bus = data;
        struct intel_uncore *uncore = &bus->dev_priv->uncore;
        u32 reserved = get_reserved(bus);

        intel_uncore_write_notrace(uncore,
                                   bus->gpio_reg,
                                   reserved | GPIO_DATA_DIR_MASK);
        intel_uncore_write_notrace(uncore, bus->gpio_reg, reserved);

        return (intel_uncore_read_notrace(uncore, bus->gpio_reg) &
                GPIO_DATA_VAL_IN) != 0;
}

static void set_clock(void *data, int state_high)
{
        struct intel_gmbus *bus = data;
        struct intel_uncore *uncore = &bus->dev_priv->uncore;
        u32 reserved = get_reserved(bus);
        u32 clock_bits;

        if (state_high)
                clock_bits = GPIO_CLOCK_DIR_IN | GPIO_CLOCK_DIR_MASK;
        else
                clock_bits = GPIO_CLOCK_DIR_OUT | GPIO_CLOCK_DIR_MASK |
                             GPIO_CLOCK_VAL_MASK;

        intel_uncore_write_notrace(uncore,
                                   bus->gpio_reg,
                                   reserved | clock_bits);
        intel_uncore_posting_read(uncore, bus->gpio_reg);
}

static void set_data(void *data, int state_high)
{
        struct intel_gmbus *bus = data;
        struct intel_uncore *uncore = &bus->dev_priv->uncore;
        u32 reserved = get_reserved(bus);
        u32 data_bits;

        if (state_high)
                data_bits = GPIO_DATA_DIR_IN | GPIO_DATA_DIR_MASK;
        else
                data_bits = GPIO_DATA_DIR_OUT | GPIO_DATA_DIR_MASK |
                        GPIO_DATA_VAL_MASK;

        intel_uncore_write_notrace(uncore, bus->gpio_reg, reserved | data_bits);
        intel_uncore_posting_read(uncore, bus->gpio_reg);
}

static int
intel_gpio_pre_xfer(struct i2c_adapter *adapter)
{
        struct intel_gmbus *bus = container_of(adapter,
                                               struct intel_gmbus,
                                               adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        intel_gmbus_reset(dev_priv);

        if (IS_PINEVIEW(dev_priv))
                pnv_gmbus_clock_gating(dev_priv, false);

        set_data(bus, 1);
        set_clock(bus, 1);
        udelay(I2C_RISEFALL_TIME);
        return 0;
}

static void
intel_gpio_post_xfer(struct i2c_adapter *adapter)
{
        struct intel_gmbus *bus = container_of(adapter,
                                               struct intel_gmbus,
                                               adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        set_data(bus, 1);
        set_clock(bus, 1);

        if (IS_PINEVIEW(dev_priv))
                pnv_gmbus_clock_gating(dev_priv, true);
}

static void
intel_gpio_setup(struct intel_gmbus *bus, unsigned int pin)
{
        struct drm_i915_private *dev_priv = bus->dev_priv;
        struct i2c_algo_bit_data *algo;

        algo = &bus->bit_algo;

        bus->gpio_reg = GPIO(get_gmbus_pin(dev_priv, pin)->gpio);
        bus->adapter.algo_data = algo;
        algo->setsda = set_data;
        algo->setscl = set_clock;
        algo->getsda = get_data;
        algo->getscl = get_clock;
        algo->pre_xfer = intel_gpio_pre_xfer;
        algo->post_xfer = intel_gpio_post_xfer;
        algo->udelay = I2C_RISEFALL_TIME;
        algo->timeout = usecs_to_jiffies(2200);
        algo->data = bus;
}

static int gmbus_wait(struct drm_i915_private *dev_priv, u32 status, u32 irq_en)
{
        DEFINE_WAIT(wait);
        u32 gmbus2;
        int ret;

        /* Important: The hw handles only the first bit, so set only one! Since
         * we also need to check for NAKs besides the hw ready/idle signal, we
         * need to wake up periodically and check that ourselves.
         */
        if (!HAS_GMBUS_IRQ(dev_priv))
                irq_en = 0;

        add_wait_queue(&dev_priv->gmbus_wait_queue, &wait);
        I915_WRITE_FW(GMBUS4, irq_en);

        status |= GMBUS_SATOER;
        ret = wait_for_us((gmbus2 = I915_READ_FW(GMBUS2)) & status, 2);
        if (ret)
                ret = wait_for((gmbus2 = I915_READ_FW(GMBUS2)) & status, 50);

        I915_WRITE_FW(GMBUS4, 0);
        remove_wait_queue(&dev_priv->gmbus_wait_queue, &wait);

        if (gmbus2 & GMBUS_SATOER)
                return -ENXIO;

        return ret;
}

static int
gmbus_wait_idle(struct drm_i915_private *dev_priv)
{
        DEFINE_WAIT(wait);
        u32 irq_enable;
        int ret;

        /* Important: The hw handles only the first bit, so set only one! */
        irq_enable = 0;
        if (HAS_GMBUS_IRQ(dev_priv))
                irq_enable = GMBUS_IDLE_EN;

        add_wait_queue(&dev_priv->gmbus_wait_queue, &wait);
        I915_WRITE_FW(GMBUS4, irq_enable);

        ret = intel_wait_for_register_fw(&dev_priv->uncore,
                                         GMBUS2, GMBUS_ACTIVE, 0,
                                         10);

        I915_WRITE_FW(GMBUS4, 0);
        remove_wait_queue(&dev_priv->gmbus_wait_queue, &wait);

        return ret;
}

static inline
unsigned int gmbus_max_xfer_size(struct drm_i915_private *dev_priv)
{
        return INTEL_GEN(dev_priv) >= 9 ? GEN9_GMBUS_BYTE_COUNT_MAX :
               GMBUS_BYTE_COUNT_MAX;
}

static int
gmbus_xfer_read_chunk(struct drm_i915_private *dev_priv,
                      unsigned short addr, u8 *buf, unsigned int len,
                      u32 gmbus0_reg, u32 gmbus1_index)
{
        unsigned int size = len;
        bool burst_read = len > gmbus_max_xfer_size(dev_priv);
        bool extra_byte_added = false;

        if (burst_read) {
                /*
                 * As per HW Spec, for 512Bytes need to read extra Byte and
                 * Ignore the extra byte read.
                 */
                if (len == 512) {
                        extra_byte_added = true;
                        len++;
                }
                size = len % 256 + 256;
                I915_WRITE_FW(GMBUS0, gmbus0_reg | GMBUS_BYTE_CNT_OVERRIDE);
        }

        I915_WRITE_FW(GMBUS1,
                      gmbus1_index |
                      GMBUS_CYCLE_WAIT |
                      (size << GMBUS_BYTE_COUNT_SHIFT) |
                      (addr << GMBUS_SLAVE_ADDR_SHIFT) |
                      GMBUS_SLAVE_READ | GMBUS_SW_RDY);
        while (len) {
                int ret;
                u32 val, loop = 0;

                ret = gmbus_wait(dev_priv, GMBUS_HW_RDY, GMBUS_HW_RDY_EN);
                if (ret)
                        return ret;

                val = I915_READ_FW(GMBUS3);
                do {
                        if (extra_byte_added && len == 1)
                                break;

                        *buf++ = val & 0xff;
                        val >>= 8;
                } while (--len && ++loop < 4);

                if (burst_read && len == size - 4)
                        /* Reset the override bit */
                        I915_WRITE_FW(GMBUS0, gmbus0_reg);
        }

        return 0;
}

/*
 * HW spec says that 512Bytes in Burst read need special treatment.
 * But it doesn't talk about other multiple of 256Bytes. And couldn't locate
 * an I2C slave, which supports such a lengthy burst read too for experiments.
 *
 * So until things get clarified on HW support, to avoid the burst read length
 * in fold of 256Bytes except 512, max burst read length is fixed at 767Bytes.
 */
#define INTEL_GMBUS_BURST_READ_MAX_LEN          767U

static int
gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
                u32 gmbus0_reg, u32 gmbus1_index)
{
        u8 *buf = msg->buf;
        unsigned int rx_size = msg->len;
        unsigned int len;
        int ret;

        do {
                if (HAS_GMBUS_BURST_READ(dev_priv))
                        len = min(rx_size, INTEL_GMBUS_BURST_READ_MAX_LEN);
                else
                        len = min(rx_size, gmbus_max_xfer_size(dev_priv));

                ret = gmbus_xfer_read_chunk(dev_priv, msg->addr, buf, len,
                                            gmbus0_reg, gmbus1_index);
                if (ret)
                        return ret;

                rx_size -= len;
                buf += len;
        } while (rx_size != 0);

        return 0;
}

static int
gmbus_xfer_write_chunk(struct drm_i915_private *dev_priv,
                       unsigned short addr, u8 *buf, unsigned int len,
                       u32 gmbus1_index)
{
        unsigned int chunk_size = len;
        u32 val, loop;

        val = loop = 0;
        while (len && loop < 4) {
                val |= *buf++ << (8 * loop++);
                len -= 1;
        }

        I915_WRITE_FW(GMBUS3, val);
        I915_WRITE_FW(GMBUS1,
                      gmbus1_index | GMBUS_CYCLE_WAIT |
                      (chunk_size << GMBUS_BYTE_COUNT_SHIFT) |
                      (addr << GMBUS_SLAVE_ADDR_SHIFT) |
                      GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
        while (len) {
                int ret;

                val = loop = 0;
                do {
                        val |= *buf++ << (8 * loop);
                } while (--len && ++loop < 4);

                I915_WRITE_FW(GMBUS3, val);

                ret = gmbus_wait(dev_priv, GMBUS_HW_RDY, GMBUS_HW_RDY_EN);
                if (ret)
                        return ret;
        }

        return 0;
}

static int
gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
                 u32 gmbus1_index)
{
        u8 *buf = msg->buf;
        unsigned int tx_size = msg->len;
        unsigned int len;
        int ret;

        do {
                len = min(tx_size, gmbus_max_xfer_size(dev_priv));

                ret = gmbus_xfer_write_chunk(dev_priv, msg->addr, buf, len,
                                             gmbus1_index);
                if (ret)
                        return ret;

                buf += len;
                tx_size -= len;
        } while (tx_size != 0);

        return 0;
}

/*
 * The gmbus controller can combine a 1 or 2 byte write with another read/write
 * that immediately follows it by using an "INDEX" cycle.
 */
static bool
gmbus_is_index_xfer(struct i2c_msg *msgs, int i, int num)
{
        return (i + 1 < num &&
                msgs[i].addr == msgs[i + 1].addr &&
                !(msgs[i].flags & I2C_M_RD) &&
                (msgs[i].len == 1 || msgs[i].len == 2) &&
                msgs[i + 1].len > 0);
}

static int
gmbus_index_xfer(struct drm_i915_private *dev_priv, struct i2c_msg *msgs,
                 u32 gmbus0_reg)
{
        u32 gmbus1_index = 0;
        u32 gmbus5 = 0;
        int ret;

        if (msgs[0].len == 2)
                gmbus5 = GMBUS_2BYTE_INDEX_EN |
                         msgs[0].buf[1] | (msgs[0].buf[0] << 8);
        if (msgs[0].len == 1)
                gmbus1_index = GMBUS_CYCLE_INDEX |
                               (msgs[0].buf[0] << GMBUS_SLAVE_INDEX_SHIFT);

        /* GMBUS5 holds 16-bit index */
        if (gmbus5)
                I915_WRITE_FW(GMBUS5, gmbus5);

        if (msgs[1].flags & I2C_M_RD)
                ret = gmbus_xfer_read(dev_priv, &msgs[1], gmbus0_reg,
                                      gmbus1_index);
        else
                ret = gmbus_xfer_write(dev_priv, &msgs[1], gmbus1_index);

        /* Clear GMBUS5 after each index transfer */
        if (gmbus5)
                I915_WRITE_FW(GMBUS5, 0);

        return ret;
}

static int
do_gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num,
              u32 gmbus0_source)
{
        struct intel_gmbus *bus = container_of(adapter,
                                               struct intel_gmbus,
                                               adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;
        int i = 0, inc, try = 0;
        int ret = 0;

        /* Display WA #0868: skl,bxt,kbl,cfl,glk,cnl */
        if (IS_GEN9_LP(dev_priv))
                bxt_gmbus_clock_gating(dev_priv, false);
        else if (HAS_PCH_SPT(dev_priv) || HAS_PCH_CNP(dev_priv))
                pch_gmbus_clock_gating(dev_priv, false);

retry:
        I915_WRITE_FW(GMBUS0, gmbus0_source | bus->reg0);

        for (; i < num; i += inc) {
                inc = 1;
                if (gmbus_is_index_xfer(msgs, i, num)) {
                        ret = gmbus_index_xfer(dev_priv, &msgs[i],
                                               gmbus0_source | bus->reg0);
                        inc = 2; /* an index transmission is two msgs */
                } else if (msgs[i].flags & I2C_M_RD) {
                        ret = gmbus_xfer_read(dev_priv, &msgs[i],
                                              gmbus0_source | bus->reg0, 0);
                } else {
                        ret = gmbus_xfer_write(dev_priv, &msgs[i], 0);
                }

                if (!ret)
                        ret = gmbus_wait(dev_priv,
                                         GMBUS_HW_WAIT_PHASE, GMBUS_HW_WAIT_EN);
                if (ret == -ETIMEDOUT)
                        goto timeout;
                else if (ret)
                        goto clear_err;
        }

        /* Generate a STOP condition on the bus. Note that gmbus can't generata
         * a STOP on the very first cycle. To simplify the code we
         * unconditionally generate the STOP condition with an additional gmbus
         * cycle. */
        I915_WRITE_FW(GMBUS1, GMBUS_CYCLE_STOP | GMBUS_SW_RDY);

        /* Mark the GMBUS interface as disabled after waiting for idle.
         * We will re-enable it at the start of the next xfer,
         * till then let it sleep.
         */
        if (gmbus_wait_idle(dev_priv)) {
                DRM_DEBUG_KMS("GMBUS [%s] timed out waiting for idle\n",
                         adapter->name);
                ret = -ETIMEDOUT;
        }
        I915_WRITE_FW(GMBUS0, 0);
        ret = ret ?: i;
        goto out;

clear_err:
        /*
         * Wait for bus to IDLE before clearing NAK.
         * If we clear the NAK while bus is still active, then it will stay
         * active and the next transaction may fail.
         *
         * If no ACK is received during the address phase of a transaction, the
         * adapter must report -ENXIO. It is not clear what to return if no ACK
         * is received at other times. But we have to be careful to not return
         * spurious -ENXIO because that will prevent i2c and drm edid functions
         * from retrying. So return -ENXIO only when gmbus properly quiescents -
         * timing out seems to happen when there _is_ a ddc chip present, but
         * it's slow responding and only answers on the 2nd retry.
         */
        ret = -ENXIO;
        if (gmbus_wait_idle(dev_priv)) {
                DRM_DEBUG_KMS("GMBUS [%s] timed out after NAK\n",
                              adapter->name);
                ret = -ETIMEDOUT;
        }

        /* Toggle the Software Clear Interrupt bit. This has the effect
         * of resetting the GMBUS controller and so clearing the
         * BUS_ERROR raised by the slave's NAK.
         */
        I915_WRITE_FW(GMBUS1, GMBUS_SW_CLR_INT);
        I915_WRITE_FW(GMBUS1, 0);
        I915_WRITE_FW(GMBUS0, 0);

        DRM_DEBUG_KMS("GMBUS [%s] NAK for addr: %04x %c(%d)\n",
                         adapter->name, msgs[i].addr,
                         (msgs[i].flags & I2C_M_RD) ? 'r' : 'w', msgs[i].len);

        /*
         * Passive adapters sometimes NAK the first probe. Retry the first
         * message once on -ENXIO for GMBUS transfers; the bit banging algorithm
         * has retries internally. See also the retry loop in
         * drm_do_probe_ddc_edid, which bails out on the first -ENXIO.
         */
        if (ret == -ENXIO && i == 0 && try++ == 0) {
                DRM_DEBUG_KMS("GMBUS [%s] NAK on first message, retry\n",
                              adapter->name);
                goto retry;
        }

        goto out;

timeout:
        DRM_DEBUG_KMS("GMBUS [%s] timed out, falling back to bit banging on pin %d\n",
                      bus->adapter.name, bus->reg0 & 0xff);
        I915_WRITE_FW(GMBUS0, 0);

        /*
         * Hardware may not support GMBUS over these pins? Try GPIO bitbanging
         * instead. Use EAGAIN to have i2c core retry.
         */
        ret = -EAGAIN;

out:
        /* Display WA #0868: skl,bxt,kbl,cfl,glk,cnl */
        if (IS_GEN9_LP(dev_priv))
                bxt_gmbus_clock_gating(dev_priv, true);
        else if (HAS_PCH_SPT(dev_priv) || HAS_PCH_CNP(dev_priv))
                pch_gmbus_clock_gating(dev_priv, true);

        return ret;
}

static int
gmbus_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs, int num)
{
        struct intel_gmbus *bus =
                container_of(adapter, struct intel_gmbus, adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;
        intel_wakeref_t wakeref;
        int ret;

        wakeref = intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);

        if (bus->force_bit) {
                ret = i2c_bit_algo.master_xfer(adapter, msgs, num);
                if (ret < 0)
                        bus->force_bit &= ~GMBUS_FORCE_BIT_RETRY;
        } else {
                ret = do_gmbus_xfer(adapter, msgs, num, 0);
                if (ret == -EAGAIN)
                        bus->force_bit |= GMBUS_FORCE_BIT_RETRY;
        }

        intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS, wakeref);

        return ret;
}

int intel_gmbus_output_aksv(struct i2c_adapter *adapter)
{
        struct intel_gmbus *bus =
                container_of(adapter, struct intel_gmbus, adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;
        u8 cmd = DRM_HDCP_DDC_AKSV;
        u8 buf[DRM_HDCP_KSV_LEN] = { 0 };
        struct i2c_msg msgs[] = {
                {
                        .addr = DRM_HDCP_DDC_ADDR,
                        .flags = 0,
                        .len = sizeof(cmd),
                        .buf = &cmd,
                },
                {
                        .addr = DRM_HDCP_DDC_ADDR,
                        .flags = 0,
                        .len = sizeof(buf),
                        .buf = buf,
                }
        };
        intel_wakeref_t wakeref;
        int ret;

        wakeref = intel_display_power_get(dev_priv, POWER_DOMAIN_GMBUS);
        mutex_lock(&dev_priv->gmbus_mutex);

        /*
         * In order to output Aksv to the receiver, use an indexed write to
         * pass the i2c command, and tell GMBUS to use the HW-provided value
         * instead of sourcing GMBUS3 for the data.
         */
        ret = do_gmbus_xfer(adapter, msgs, ARRAY_SIZE(msgs), GMBUS_AKSV_SELECT);

        mutex_unlock(&dev_priv->gmbus_mutex);
        intel_display_power_put(dev_priv, POWER_DOMAIN_GMBUS, wakeref);

        return ret;
}

static u32 gmbus_func(struct i2c_adapter *adapter)
{
        return i2c_bit_algo.functionality(adapter) &
                (I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
                /* I2C_FUNC_10BIT_ADDR | */
                I2C_FUNC_SMBUS_READ_BLOCK_DATA |
                I2C_FUNC_SMBUS_BLOCK_PROC_CALL);
}

static const struct i2c_algorithm gmbus_algorithm = {
        .master_xfer    = gmbus_xfer,
        .functionality  = gmbus_func
};

static void gmbus_lock_bus(struct i2c_adapter *adapter,
                           unsigned int flags)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        mutex_lock(&dev_priv->gmbus_mutex);
}

static int gmbus_trylock_bus(struct i2c_adapter *adapter,
                             unsigned int flags)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        return mutex_trylock(&dev_priv->gmbus_mutex);
}

static void gmbus_unlock_bus(struct i2c_adapter *adapter,
                             unsigned int flags)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        mutex_unlock(&dev_priv->gmbus_mutex);
}

static const struct i2c_lock_operations gmbus_lock_ops = {
        .lock_bus =    gmbus_lock_bus,
        .trylock_bus = gmbus_trylock_bus,
        .unlock_bus =  gmbus_unlock_bus,
};

/**
 * intel_gmbus_setup - instantiate all Intel i2c GMBuses
 * @dev_priv: i915 device private
 */
int intel_gmbus_setup(struct drm_i915_private *dev_priv)
{
        struct pci_dev *pdev = dev_priv->drm.pdev;
        struct intel_gmbus *bus;
        unsigned int pin;
        int ret;

        if (!HAS_DISPLAY(dev_priv))
                return 0;

        if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
                dev_priv->gpio_mmio_base = VLV_DISPLAY_BASE;
        else if (!HAS_GMCH(dev_priv))
                /*
                 * Broxton uses the same PCH offsets for South Display Engine,
                 * even though it doesn't have a PCH.
                 */
                dev_priv->gpio_mmio_base = PCH_DISPLAY_BASE;

        mutex_init(&dev_priv->gmbus_mutex);
        init_waitqueue_head(&dev_priv->gmbus_wait_queue);

        for (pin = 0; pin < ARRAY_SIZE(dev_priv->gmbus); pin++) {
                if (!intel_gmbus_is_valid_pin(dev_priv, pin))
                        continue;

                bus = &dev_priv->gmbus[pin];

                bus->adapter.owner = THIS_MODULE;
                bus->adapter.class = I2C_CLASS_DDC;
                snprintf(bus->adapter.name,
                         sizeof(bus->adapter.name),
                         "i915 gmbus %s",
                         get_gmbus_pin(dev_priv, pin)->name);

                bus->adapter.dev.parent = &pdev->dev;
                bus->dev_priv = dev_priv;

                bus->adapter.algo = &gmbus_algorithm;
                bus->adapter.lock_ops = &gmbus_lock_ops;

                /*
                 * We wish to retry with bit banging
                 * after a timed out GMBUS attempt.
                 */
                bus->adapter.retries = 1;

                /* By default use a conservative clock rate */
                bus->reg0 = pin | GMBUS_RATE_100KHZ;

                /* gmbus seems to be broken on i830 */
                if (IS_I830(dev_priv))
                        bus->force_bit = 1;

                intel_gpio_setup(bus, pin);

                ret = i2c_add_adapter(&bus->adapter);
                if (ret)
                        goto err;
        }

        intel_gmbus_reset(dev_priv);

        return 0;

err:
        while (pin--) {
                if (!intel_gmbus_is_valid_pin(dev_priv, pin))
                        continue;

                bus = &dev_priv->gmbus[pin];
                i2c_del_adapter(&bus->adapter);
        }
        return ret;
}

struct i2c_adapter *intel_gmbus_get_adapter(struct drm_i915_private *dev_priv,
                                            unsigned int pin)
{
        if (WARN_ON(!intel_gmbus_is_valid_pin(dev_priv, pin)))
                return NULL;

        return &dev_priv->gmbus[pin].adapter;
}

void intel_gmbus_set_speed(struct i2c_adapter *adapter, int speed)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);

        bus->reg0 = (bus->reg0 & ~(0x3 << 8)) | speed;
}

void intel_gmbus_force_bit(struct i2c_adapter *adapter, bool force_bit)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);
        struct drm_i915_private *dev_priv = bus->dev_priv;

        mutex_lock(&dev_priv->gmbus_mutex);

        bus->force_bit += force_bit ? 1 : -1;
        DRM_DEBUG_KMS("%sabling bit-banging on %s. force bit now %d\n",
                      force_bit ? "en" : "dis", adapter->name,
                      bus->force_bit);

        mutex_unlock(&dev_priv->gmbus_mutex);
}

bool intel_gmbus_is_forced_bit(struct i2c_adapter *adapter)
{
        struct intel_gmbus *bus = to_intel_gmbus(adapter);

        return bus->force_bit;
}

void intel_gmbus_teardown(struct drm_i915_private *dev_priv)
{
        struct intel_gmbus *bus;
        unsigned int pin;

        for (pin = 0; pin < ARRAY_SIZE(dev_priv->gmbus); pin++) {
                if (!intel_gmbus_is_valid_pin(dev_priv, pin))
                        continue;

                bus = &dev_priv->gmbus[pin];
                i2c_del_adapter(&bus->adapter);
        }
}