/*
 * 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(clk)) {
		if (clk_prepare_enable(clk) == 0) {
			clock_freq = clk_get_rate(clk);
			clk_disable_unprepare(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);