/*
 * J-Core SPI controller driver
 *
 * Copyright (C) 2012-2016 Smart Energy Instruments, Inc.
 *
 * Current version by Rich Felker
 * Based loosely on initial version by Oleksandr G Zhadan
 *
 */
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/spi/spi.h>
#include <linux/clk.h>
#include <linux/err.h>
#include <linux/io.h>
#include <linux/of.h>
#include <linux/delay.h>

#define DRV_NAME        "jcore_spi"

#define CTRL_REG        0x0
#define DATA_REG        0x4

#define JCORE_SPI_CTRL_XMIT             0x02
#define JCORE_SPI_STAT_BUSY             0x02
#define JCORE_SPI_CTRL_LOOP             0x08
#define JCORE_SPI_CTRL_CS_BITS          0x15

#define JCORE_SPI_WAIT_RDY_MAX_LOOP     2000000

struct jcore_spi {
        struct spi_master *master;
        void __iomem *base;
        unsigned int cs_reg;
        unsigned int speed_reg;
        unsigned int speed_hz;
        unsigned int clock_freq;
};

static int jcore_spi_wait(void __iomem *ctrl_reg)
{
        unsigned timeout = JCORE_SPI_WAIT_RDY_MAX_LOOP;

        do {
                if (!(readl(ctrl_reg) & JCORE_SPI_STAT_BUSY))
                        return 0;
                cpu_relax();
        } while (--timeout);

        return -EBUSY;
}

static void jcore_spi_program(struct jcore_spi *hw)
{
        void __iomem *ctrl_reg = hw->base + CTRL_REG;

        if (jcore_spi_wait(ctrl_reg))
                dev_err(hw->master->dev.parent,
                        "timeout waiting to program ctrl reg.\n");

        writel(hw->cs_reg | hw->speed_reg, ctrl_reg);
}

static void jcore_spi_chipsel(struct spi_device *spi, bool value)
{
        struct jcore_spi *hw = spi_master_get_devdata(spi->master);
        u32 csbit = 1U << (2 * spi->chip_select);

        dev_dbg(hw->master->dev.parent, "chipselect %d\n", spi->chip_select);

        if (value)
                hw->cs_reg |= csbit;
        else
                hw->cs_reg &= ~csbit;

        jcore_spi_program(hw);
}

static void jcore_spi_baudrate(struct jcore_spi *hw, int speed)
{
        if (speed == hw->speed_hz) return;
        hw->speed_hz = speed;
        if (speed >= hw->clock_freq / 2)
                hw->speed_reg = 0;
        else
                hw->speed_reg = ((hw->clock_freq / 2 / speed) - 1) << 27;
        jcore_spi_program(hw);
        dev_dbg(hw->master->dev.parent, "speed=%d reg=0x%x\n",
                speed, hw->speed_reg);
}

static int jcore_spi_txrx(struct spi_master *master, struct spi_device *spi,
                          struct spi_transfer *t)
{
        struct jcore_spi *hw = spi_master_get_devdata(master);

        void __iomem *ctrl_reg = hw->base + CTRL_REG;
        void __iomem *data_reg = hw->base + DATA_REG;
        u32 xmit;

        /* data buffers */
        const unsigned char *tx;
        unsigned char *rx;
        unsigned int len;
        unsigned int count;

        jcore_spi_baudrate(hw, t->speed_hz);

        xmit = hw->cs_reg | hw->speed_reg | JCORE_SPI_CTRL_XMIT;
        tx = t->tx_buf;
        rx = t->rx_buf;
        len = t->len;

        for (count = 0; count < len; count++) {
                if (jcore_spi_wait(ctrl_reg))
                        break;

                writel(tx ? *tx++ : 0, data_reg);
                writel(xmit, ctrl_reg);

                if (jcore_spi_wait(ctrl_reg))
                        break;

                if (rx)
                        *rx++ = readl(data_reg);
        }

        spi_finalize_current_transfer(master);

        if (count < len)
                return -EREMOTEIO;

        return 0;
}

static int jcore_spi_probe(struct platform_device *pdev)
{
        struct device_node *node = pdev->dev.of_node;
        struct jcore_spi *hw;
        struct spi_master *master;
        struct resource *res;
        u32 clock_freq;
        struct clk *clk;
        int err = -ENODEV;

        master = spi_alloc_master(&pdev->dev, sizeof(struct jcore_spi));
        if (!master)
                return err;

        /* Setup the master state. */
        master->num_chipselect = 3;
        master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;
        master->transfer_one = jcore_spi_txrx;
        master->set_cs = jcore_spi_chipsel;
        master->dev.of_node = node;
        master->bus_num = pdev->id;

        hw = spi_master_get_devdata(master);
        hw->master = master;
        platform_set_drvdata(pdev, hw);

        /* Find and map our resources */
        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
        if (!res)
                goto exit_busy;
        if (!devm_request_mem_region(&pdev->dev, res->start,
                                     resource_size(res), pdev->name))
                goto exit_busy;
        hw->base = devm_ioremap_nocache(&pdev->dev, res->start,
                                        resource_size(res));
        if (!hw->base)
                goto exit_busy;

        /*
         * The SPI clock rate controlled via a configurable clock divider
         * which is applied to the reference clock. A 50 MHz reference is
         * most suitable for obtaining standard SPI clock rates, but some
         * designs may have a different reference clock, and the DT must
         * make the driver aware so that it can properly program the
         * requested rate. If the clock is omitted, 50 MHz is assumed.
         */
        clock_freq = 50000000;
        clk = devm_clk_get(&pdev->dev, "ref_clk");
        if (!IS_ERR_OR_NULL(clk)) {
                if (clk_enable(clk) == 0)
                        clock_freq = clk_get_rate(clk);
                else
                        dev_warn(&pdev->dev, "could not enable ref_clk\n");
        }
        hw->clock_freq = clock_freq;

        /* Initialize all CS bits to high. */
        hw->cs_reg = JCORE_SPI_CTRL_CS_BITS;
        jcore_spi_baudrate(hw, 400000);

        /* Register our spi controller */
        err = devm_spi_register_master(&pdev->dev, master);
        if (err)
                goto exit;

        return 0;

exit_busy:
        err = -EBUSY;
exit:
        spi_master_put(master);
        return err;
}

static const struct of_device_id jcore_spi_of_match[] = {
        { .compatible = "jcore,spi2" },
        {},
};
MODULE_DEVICE_TABLE(of, jcore_spi_of_match);

static struct platform_driver jcore_spi_driver = {
        .probe = jcore_spi_probe,
        .driver = {
                .name = DRV_NAME,
                .of_match_table = jcore_spi_of_match,
        },
};

module_platform_driver(jcore_spi_driver);

MODULE_DESCRIPTION("J-Core SPI driver");
MODULE_AUTHOR("Rich Felker <dalias@libc.org>");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:" DRV_NAME);