drivers/spi/spi-sifive.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 //
 // Copyright 2018 SiFive, Inc.
 //
 // SiFive SPI controller driver (master mode only)
 //
 // Author: SiFive, Inc.
 // sifive@sifive.com

 #include <linux/clk.h>
 #include <linux/module.h>
 #include <linux/interrupt.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/spi/spi.h>
 #include <linux/io.h>
 #include <linux/log2.h>

 #define SIFIVE_SPI_DRIVER_NAME           "sifive_spi"

 #define SIFIVE_SPI_MAX_CS                32
 #define SIFIVE_SPI_DEFAULT_DEPTH         8
 #define SIFIVE_SPI_DEFAULT_MAX_BITS      8

 /* register offsets */
 #define SIFIVE_SPI_REG_SCKDIV            0x00 /* Serial clock divisor */
 #define SIFIVE_SPI_REG_SCKMODE           0x04 /* Serial clock mode */
 #define SIFIVE_SPI_REG_CSID              0x10 /* Chip select ID */
 #define SIFIVE_SPI_REG_CSDEF             0x14 /* Chip select default */
 #define SIFIVE_SPI_REG_CSMODE            0x18 /* Chip select mode */
 #define SIFIVE_SPI_REG_DELAY0            0x28 /* Delay control 0 */
 #define SIFIVE_SPI_REG_DELAY1            0x2c /* Delay control 1 */
 #define SIFIVE_SPI_REG_FMT               0x40 /* Frame format */
 #define SIFIVE_SPI_REG_TXDATA            0x48 /* Tx FIFO data */
 #define SIFIVE_SPI_REG_RXDATA            0x4c /* Rx FIFO data */
 #define SIFIVE_SPI_REG_TXMARK            0x50 /* Tx FIFO watermark */
 #define SIFIVE_SPI_REG_RXMARK            0x54 /* Rx FIFO watermark */
 #define SIFIVE_SPI_REG_FCTRL             0x60 /* SPI flash interface control */
 #define SIFIVE_SPI_REG_FFMT              0x64 /* SPI flash instruction format */
 #define SIFIVE_SPI_REG_IE                0x70 /* Interrupt Enable Register */
 #define SIFIVE_SPI_REG_IP                0x74 /* Interrupt Pendings Register */

 /* sckdiv bits */
 #define SIFIVE_SPI_SCKDIV_DIV_MASK       0xfffU

 /* sckmode bits */
 #define SIFIVE_SPI_SCKMODE_PHA           BIT(0)
 #define SIFIVE_SPI_SCKMODE_POL           BIT(1)
 #define SIFIVE_SPI_SCKMODE_MODE_MASK     (SIFIVE_SPI_SCKMODE_PHA | \
 					  SIFIVE_SPI_SCKMODE_POL)

 /* csmode bits */
 #define SIFIVE_SPI_CSMODE_MODE_AUTO      0U
 #define SIFIVE_SPI_CSMODE_MODE_HOLD      2U
 #define SIFIVE_SPI_CSMODE_MODE_OFF       3U

 /* delay0 bits */
 #define SIFIVE_SPI_DELAY0_CSSCK(x)       ((u32)(x))
 #define SIFIVE_SPI_DELAY0_CSSCK_MASK     0xffU
 #define SIFIVE_SPI_DELAY0_SCKCS(x)       ((u32)(x) << 16)
 #define SIFIVE_SPI_DELAY0_SCKCS_MASK     (0xffU << 16)

 /* delay1 bits */
 #define SIFIVE_SPI_DELAY1_INTERCS(x)     ((u32)(x))
 #define SIFIVE_SPI_DELAY1_INTERCS_MASK   0xffU
 #define SIFIVE_SPI_DELAY1_INTERXFR(x)    ((u32)(x) << 16)
 #define SIFIVE_SPI_DELAY1_INTERXFR_MASK  (0xffU << 16)

 /* fmt bits */
 #define SIFIVE_SPI_FMT_PROTO_SINGLE      0U
 #define SIFIVE_SPI_FMT_PROTO_DUAL        1U
 #define SIFIVE_SPI_FMT_PROTO_QUAD        2U
 #define SIFIVE_SPI_FMT_PROTO_MASK        3U
 #define SIFIVE_SPI_FMT_ENDIAN            BIT(2)
 #define SIFIVE_SPI_FMT_DIR               BIT(3)
 #define SIFIVE_SPI_FMT_LEN(x)            ((u32)(x) << 16)
 #define SIFIVE_SPI_FMT_LEN_MASK          (0xfU << 16)

 /* txdata bits */
 #define SIFIVE_SPI_TXDATA_DATA_MASK      0xffU
 #define SIFIVE_SPI_TXDATA_FULL           BIT(31)

 /* rxdata bits */
 #define SIFIVE_SPI_RXDATA_DATA_MASK      0xffU
 #define SIFIVE_SPI_RXDATA_EMPTY          BIT(31)

 /* ie and ip bits */
 #define SIFIVE_SPI_IP_TXWM               BIT(0)
 #define SIFIVE_SPI_IP_RXWM               BIT(1)

 struct sifive_spi {
 	void __iomem      *regs;        /* virt. address of control registers */
 	struct clk        *clk;         /* bus clock */
 	unsigned int      fifo_depth;   /* fifo depth in words */
 	u32               cs_inactive;  /* level of the CS pins when inactive */
 	struct completion done;         /* wake-up from interrupt */
 };

 static void sifive_spi_write(struct sifive_spi *spi, int offset, u32 value)
 {
 	iowrite32(value, spi->regs + offset);
 }

 static u32 sifive_spi_read(struct sifive_spi *spi, int offset)
 {
 	return ioread32(spi->regs + offset);
 }

 static void sifive_spi_init(struct sifive_spi *spi)
 {
 	/* Watermark interrupts are disabled by default */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);

 	/* Default watermark FIFO threshold values */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_TXMARK, 1);
 	sifive_spi_write(spi, SIFIVE_SPI_REG_RXMARK, 0);

 	/* Set CS/SCK Delays and Inactive Time to defaults */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_DELAY0,
 			 SIFIVE_SPI_DELAY0_CSSCK(1) |
 			 SIFIVE_SPI_DELAY0_SCKCS(1));
 	sifive_spi_write(spi, SIFIVE_SPI_REG_DELAY1,
 			 SIFIVE_SPI_DELAY1_INTERCS(1) |
 			 SIFIVE_SPI_DELAY1_INTERXFR(0));

 	/* Exit specialized memory-mapped SPI flash mode */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_FCTRL, 0);
 }

 static int
 sifive_spi_prepare_message(struct spi_master *master, struct spi_message *msg)
 {
 	struct sifive_spi *spi = spi_master_get_devdata(master);
 	struct spi_device *device = msg->spi;

 	/* Update the chip select polarity */
 	if (device->mode & SPI_CS_HIGH)
 		spi->cs_inactive &= ~BIT(device->chip_select);
 	else
 		spi->cs_inactive |= BIT(device->chip_select);
 	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, spi->cs_inactive);

 	/* Select the correct device */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_CSID, device->chip_select);

 	/* Set clock mode */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_SCKMODE,
 			 device->mode & SIFIVE_SPI_SCKMODE_MODE_MASK);

 	return 0;
 }

 static void sifive_spi_set_cs(struct spi_device *device, bool is_high)
 {
 	struct sifive_spi *spi = spi_master_get_devdata(device->master);

 	/* Reverse polarity is handled by SCMR/CPOL. Not inverted CS. */
 	if (device->mode & SPI_CS_HIGH)
 		is_high = !is_high;

 	sifive_spi_write(spi, SIFIVE_SPI_REG_CSMODE, is_high ?
 			 SIFIVE_SPI_CSMODE_MODE_AUTO :
 			 SIFIVE_SPI_CSMODE_MODE_HOLD);
 }

 static int
 sifive_spi_prep_transfer(struct sifive_spi *spi, struct spi_device *device,
 			 struct spi_transfer *t)
 {
 	u32 cr;
 	unsigned int mode;

 	/* Calculate and program the clock rate */
 	cr = DIV_ROUND_UP(clk_get_rate(spi->clk) >> 1, t->speed_hz) - 1;
 	cr &= SIFIVE_SPI_SCKDIV_DIV_MASK;
 	sifive_spi_write(spi, SIFIVE_SPI_REG_SCKDIV, cr);

 	mode = max_t(unsigned int, t->rx_nbits, t->tx_nbits);

 	/* Set frame format */
 	cr = SIFIVE_SPI_FMT_LEN(t->bits_per_word);
 	switch (mode) {
 	case SPI_NBITS_QUAD:
 		cr |= SIFIVE_SPI_FMT_PROTO_QUAD;
 		break;
 	case SPI_NBITS_DUAL:
 		cr |= SIFIVE_SPI_FMT_PROTO_DUAL;
 		break;
 	default:
 		cr |= SIFIVE_SPI_FMT_PROTO_SINGLE;
 		break;
 	}
 	if (device->mode & SPI_LSB_FIRST)
 		cr |= SIFIVE_SPI_FMT_ENDIAN;
 	if (!t->rx_buf)
 		cr |= SIFIVE_SPI_FMT_DIR;
 	sifive_spi_write(spi, SIFIVE_SPI_REG_FMT, cr);

 	/* We will want to poll if the time we need to wait is
 	 * less than the context switching time.
 	 * Let's call that threshold 5us. The operation will take:
 	 *    (8/mode) * fifo_depth / hz <= 5 * 10^-6
 	 *    1600000 * fifo_depth <= hz * mode
 	 */
 	return 1600000 * spi->fifo_depth <= t->speed_hz * mode;
 }

 static irqreturn_t sifive_spi_irq(int irq, void *dev_id)
 {
 	struct sifive_spi *spi = dev_id;
 	u32 ip = sifive_spi_read(spi, SIFIVE_SPI_REG_IP);

 	if (ip & (SIFIVE_SPI_IP_TXWM | SIFIVE_SPI_IP_RXWM)) {
 		/* Disable interrupts until next transfer */
 		sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);
 		complete(&spi->done);
 		return IRQ_HANDLED;
 	}

 	return IRQ_NONE;
 }

 static void sifive_spi_wait(struct sifive_spi *spi, u32 bit, int poll)
 {
 	if (poll) {
 		u32 cr;

 		do {
 			cr = sifive_spi_read(spi, SIFIVE_SPI_REG_IP);
 		} while (!(cr & bit));
 	} else {
 		reinit_completion(&spi->done);
 		sifive_spi_write(spi, SIFIVE_SPI_REG_IE, bit);
 		wait_for_completion(&spi->done);
 	}
 }

 static void sifive_spi_tx(struct sifive_spi *spi, const u8 *tx_ptr)
 {
 	WARN_ON_ONCE((sifive_spi_read(spi, SIFIVE_SPI_REG_TXDATA)
 				& SIFIVE_SPI_TXDATA_FULL) != 0);
 	sifive_spi_write(spi, SIFIVE_SPI_REG_TXDATA,
 			 *tx_ptr & SIFIVE_SPI_TXDATA_DATA_MASK);
 }

 static void sifive_spi_rx(struct sifive_spi *spi, u8 *rx_ptr)
 {
 	u32 data = sifive_spi_read(spi, SIFIVE_SPI_REG_RXDATA);

 	WARN_ON_ONCE((data & SIFIVE_SPI_RXDATA_EMPTY) != 0);
 	*rx_ptr = data & SIFIVE_SPI_RXDATA_DATA_MASK;
 }

 static int
 sifive_spi_transfer_one(struct spi_master *master, struct spi_device *device,
 			struct spi_transfer *t)
 {
 	struct sifive_spi *spi = spi_master_get_devdata(master);
 	int poll = sifive_spi_prep_transfer(spi, device, t);
 	const u8 *tx_ptr = t->tx_buf;
 	u8 *rx_ptr = t->rx_buf;
 	unsigned int remaining_words = t->len;

 	while (remaining_words) {
 		unsigned int n_words = min(remaining_words, spi->fifo_depth);
 		unsigned int i;

 		/* Enqueue n_words for transmission */
 		for (i = 0; i < n_words; i++)
 			sifive_spi_tx(spi, tx_ptr++);

 		if (rx_ptr) {
 			/* Wait for transmission + reception to complete */
 			sifive_spi_write(spi, SIFIVE_SPI_REG_RXMARK,
 					 n_words - 1);
 			sifive_spi_wait(spi, SIFIVE_SPI_IP_RXWM, poll);

 			/* Read out all the data from the RX FIFO */
 			for (i = 0; i < n_words; i++)
 				sifive_spi_rx(spi, rx_ptr++);
 		} else {
 			/* Wait for transmission to complete */
 			sifive_spi_wait(spi, SIFIVE_SPI_IP_TXWM, poll);
 		}

 		remaining_words -= n_words;
 	}

 	return 0;
 }

 static int sifive_spi_probe(struct platform_device *pdev)
 {
 	struct sifive_spi *spi;
 	int ret, irq, num_cs;
 	u32 cs_bits, max_bits_per_word;
 	struct spi_master *master;

 	master = spi_alloc_master(&pdev->dev, sizeof(struct sifive_spi));
 	if (!master) {
 		dev_err(&pdev->dev, "out of memory\n");
 		return -ENOMEM;
 	}

 	spi = spi_master_get_devdata(master);
 	init_completion(&spi->done);
 	platform_set_drvdata(pdev, master);

 	spi->regs = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(spi->regs)) {
 		ret = PTR_ERR(spi->regs);
 		goto put_master;
 	}

 	spi->clk = devm_clk_get(&pdev->dev, NULL);
 	if (IS_ERR(spi->clk)) {
 		dev_err(&pdev->dev, "Unable to find bus clock\n");
 		ret = PTR_ERR(spi->clk);
 		goto put_master;
 	}

 	irq = platform_get_irq(pdev, 0);
 	if (irq < 0) {
 		ret = irq;
 		goto put_master;
 	}

 	/* Optional parameters */
 	ret =
 	  of_property_read_u32(pdev->dev.of_node, "sifive,fifo-depth",
 			       &spi->fifo_depth);
 	if (ret < 0)
 		spi->fifo_depth = SIFIVE_SPI_DEFAULT_DEPTH;

 	ret =
 	  of_property_read_u32(pdev->dev.of_node, "sifive,max-bits-per-word",
 			       &max_bits_per_word);

 	if (!ret && max_bits_per_word < 8) {
 		dev_err(&pdev->dev, "Only 8bit SPI words supported by the driver\n");
 		ret = -EINVAL;
 		goto put_master;
 	}

 	/* Spin up the bus clock before hitting registers */
 	ret = clk_prepare_enable(spi->clk);
 	if (ret) {
 		dev_err(&pdev->dev, "Unable to enable bus clock\n");
 		goto put_master;
 	}

 	/* probe the number of CS lines */
 	spi->cs_inactive = sifive_spi_read(spi, SIFIVE_SPI_REG_CSDEF);
 	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, 0xffffffffU);
 	cs_bits = sifive_spi_read(spi, SIFIVE_SPI_REG_CSDEF);
 	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, spi->cs_inactive);
 	if (!cs_bits) {
 		dev_err(&pdev->dev, "Could not auto probe CS lines\n");
 		ret = -EINVAL;
 		goto disable_clk;
 	}

 	num_cs = ilog2(cs_bits) + 1;
 	if (num_cs > SIFIVE_SPI_MAX_CS) {
 		dev_err(&pdev->dev, "Invalid number of spi slaves\n");
 		ret = -EINVAL;
 		goto disable_clk;
 	}

 	/* Define our master */
 	master->dev.of_node = pdev->dev.of_node;
 	master->bus_num = pdev->id;
 	master->num_chipselect = num_cs;
 	master->mode_bits = SPI_CPHA | SPI_CPOL
 			  | SPI_CS_HIGH | SPI_LSB_FIRST
 			  | SPI_TX_DUAL | SPI_TX_QUAD
 			  | SPI_RX_DUAL | SPI_RX_QUAD;
 	/* TODO: add driver support for bits_per_word < 8
 	 * we need to "left-align" the bits (unless SPI_LSB_FIRST)
 	 */
 	master->bits_per_word_mask = SPI_BPW_MASK(8);
 	master->flags = SPI_CONTROLLER_MUST_TX | SPI_MASTER_GPIO_SS;
 	master->prepare_message = sifive_spi_prepare_message;
 	master->set_cs = sifive_spi_set_cs;
 	master->transfer_one = sifive_spi_transfer_one;

 	pdev->dev.dma_mask = NULL;
 	/* Configure the SPI master hardware */
 	sifive_spi_init(spi);

 	/* Register for SPI Interrupt */
 	ret = devm_request_irq(&pdev->dev, irq, sifive_spi_irq, 0,
 			       dev_name(&pdev->dev), spi);
 	if (ret) {
 		dev_err(&pdev->dev, "Unable to bind to interrupt\n");
 		goto disable_clk;
 	}

 	dev_info(&pdev->dev, "mapped; irq=%d, cs=%d\n",
 		 irq, master->num_chipselect);

 	ret = devm_spi_register_master(&pdev->dev, master);
 	if (ret < 0) {
 		dev_err(&pdev->dev, "spi_register_master failed\n");
 		goto disable_clk;
 	}

 	return 0;

 disable_clk:
 	clk_disable_unprepare(spi->clk);
 put_master:
 	spi_master_put(master);

 	return ret;
 }

 static int sifive_spi_remove(struct platform_device *pdev)
 {
 	struct spi_master *master = platform_get_drvdata(pdev);
 	struct sifive_spi *spi = spi_master_get_devdata(master);

 	/* Disable all the interrupts just in case */
 	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);
 	clk_disable_unprepare(spi->clk);

 	return 0;
 }

 static const struct of_device_id sifive_spi_of_match[] = {
 	{ .compatible = "sifive,spi0", },
 	{}
 };
 MODULE_DEVICE_TABLE(of, sifive_spi_of_match);

 static struct platform_driver sifive_spi_driver = {
 	.probe = sifive_spi_probe,
 	.remove = sifive_spi_remove,
 	.driver = {
 		.name = SIFIVE_SPI_DRIVER_NAME,
 		.of_match_table = sifive_spi_of_match,
 	},
 };
 module_platform_driver(sifive_spi_driver);

 MODULE_AUTHOR("SiFive, Inc. <sifive@sifive.com>");
 MODULE_DESCRIPTION("SiFive SPI driver");
 MODULE_LICENSE("GPL");
	// SPDX-License-Identifier: GPL-2.0
	//
	// Copyright 2018 SiFive, Inc.
	//
	// SiFive SPI controller driver (master mode only)
	//
	// Author: SiFive, Inc.
	// sifive@sifive.com

	#include <linux/clk.h>
	#include <linux/module.h>
	#include <linux/interrupt.h>
	#include <linux/of.h>
	#include <linux/platform_device.h>
	#include <linux/spi/spi.h>
	#include <linux/io.h>
	#include <linux/log2.h>

	#define SIFIVE_SPI_DRIVER_NAME "sifive_spi"

	#define SIFIVE_SPI_MAX_CS 32
	#define SIFIVE_SPI_DEFAULT_DEPTH 8
	#define SIFIVE_SPI_DEFAULT_MAX_BITS 8

	/* register offsets */
	#define SIFIVE_SPI_REG_SCKDIV 0x00 /* Serial clock divisor */
	#define SIFIVE_SPI_REG_SCKMODE 0x04 /* Serial clock mode */
	#define SIFIVE_SPI_REG_CSID 0x10 /* Chip select ID */
	#define SIFIVE_SPI_REG_CSDEF 0x14 /* Chip select default */
	#define SIFIVE_SPI_REG_CSMODE 0x18 /* Chip select mode */
	#define SIFIVE_SPI_REG_DELAY0 0x28 /* Delay control 0 */
	#define SIFIVE_SPI_REG_DELAY1 0x2c /* Delay control 1 */
	#define SIFIVE_SPI_REG_FMT 0x40 /* Frame format */
	#define SIFIVE_SPI_REG_TXDATA 0x48 /* Tx FIFO data */
	#define SIFIVE_SPI_REG_RXDATA 0x4c /* Rx FIFO data */
	#define SIFIVE_SPI_REG_TXMARK 0x50 /* Tx FIFO watermark */
	#define SIFIVE_SPI_REG_RXMARK 0x54 /* Rx FIFO watermark */
	#define SIFIVE_SPI_REG_FCTRL 0x60 /* SPI flash interface control */
	#define SIFIVE_SPI_REG_FFMT 0x64 /* SPI flash instruction format */
	#define SIFIVE_SPI_REG_IE 0x70 /* Interrupt Enable Register */
	#define SIFIVE_SPI_REG_IP 0x74 /* Interrupt Pendings Register */

	/* sckdiv bits */
	#define SIFIVE_SPI_SCKDIV_DIV_MASK 0xfffU

	/* sckmode bits */
	#define SIFIVE_SPI_SCKMODE_PHA BIT(0)
	#define SIFIVE_SPI_SCKMODE_POL BIT(1)
	#define SIFIVE_SPI_SCKMODE_MODE_MASK (SIFIVE_SPI_SCKMODE_PHA \| \
	SIFIVE_SPI_SCKMODE_POL)

	/* csmode bits */
	#define SIFIVE_SPI_CSMODE_MODE_AUTO 0U
	#define SIFIVE_SPI_CSMODE_MODE_HOLD 2U
	#define SIFIVE_SPI_CSMODE_MODE_OFF 3U

	/* delay0 bits */
	#define SIFIVE_SPI_DELAY0_CSSCK(x) ((u32)(x))
	#define SIFIVE_SPI_DELAY0_CSSCK_MASK 0xffU
	#define SIFIVE_SPI_DELAY0_SCKCS(x) ((u32)(x) << 16)
	#define SIFIVE_SPI_DELAY0_SCKCS_MASK (0xffU << 16)

	/* delay1 bits */
	#define SIFIVE_SPI_DELAY1_INTERCS(x) ((u32)(x))
	#define SIFIVE_SPI_DELAY1_INTERCS_MASK 0xffU
	#define SIFIVE_SPI_DELAY1_INTERXFR(x) ((u32)(x) << 16)
	#define SIFIVE_SPI_DELAY1_INTERXFR_MASK (0xffU << 16)

	/* fmt bits */
	#define SIFIVE_SPI_FMT_PROTO_SINGLE 0U
	#define SIFIVE_SPI_FMT_PROTO_DUAL 1U
	#define SIFIVE_SPI_FMT_PROTO_QUAD 2U
	#define SIFIVE_SPI_FMT_PROTO_MASK 3U
	#define SIFIVE_SPI_FMT_ENDIAN BIT(2)
	#define SIFIVE_SPI_FMT_DIR BIT(3)
	#define SIFIVE_SPI_FMT_LEN(x) ((u32)(x) << 16)
	#define SIFIVE_SPI_FMT_LEN_MASK (0xfU << 16)

	/* txdata bits */
	#define SIFIVE_SPI_TXDATA_DATA_MASK 0xffU
	#define SIFIVE_SPI_TXDATA_FULL BIT(31)

	/* rxdata bits */
	#define SIFIVE_SPI_RXDATA_DATA_MASK 0xffU
	#define SIFIVE_SPI_RXDATA_EMPTY BIT(31)

	/* ie and ip bits */
	#define SIFIVE_SPI_IP_TXWM BIT(0)
	#define SIFIVE_SPI_IP_RXWM BIT(1)

	struct sifive_spi {
	void __iomem regs; / virt. address of control registers */
	struct clk clk; / bus clock */
	unsigned int fifo_depth; /* fifo depth in words */
	u32 cs_inactive; /* level of the CS pins when inactive */
	struct completion done; /* wake-up from interrupt */
	};

	static void sifive_spi_write(struct sifive_spi *spi, int offset, u32 value)
	{
	iowrite32(value, spi->regs + offset);
	}

	static u32 sifive_spi_read(struct sifive_spi *spi, int offset)
	{
	return ioread32(spi->regs + offset);
	}

	static void sifive_spi_init(struct sifive_spi *spi)
	{
	/* Watermark interrupts are disabled by default */
	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);

	/* Default watermark FIFO threshold values */
	sifive_spi_write(spi, SIFIVE_SPI_REG_TXMARK, 1);
	sifive_spi_write(spi, SIFIVE_SPI_REG_RXMARK, 0);

	/* Set CS/SCK Delays and Inactive Time to defaults */
	sifive_spi_write(spi, SIFIVE_SPI_REG_DELAY0,
	SIFIVE_SPI_DELAY0_CSSCK(1) \|
	SIFIVE_SPI_DELAY0_SCKCS(1));
	sifive_spi_write(spi, SIFIVE_SPI_REG_DELAY1,
	SIFIVE_SPI_DELAY1_INTERCS(1) \|
	SIFIVE_SPI_DELAY1_INTERXFR(0));

	/* Exit specialized memory-mapped SPI flash mode */
	sifive_spi_write(spi, SIFIVE_SPI_REG_FCTRL, 0);
	}

	static int
	sifive_spi_prepare_message(struct spi_master master, struct spi_message msg)
	{
	struct sifive_spi *spi = spi_master_get_devdata(master);
	struct spi_device *device = msg->spi;

	/* Update the chip select polarity */
	if (device->mode & SPI_CS_HIGH)
	spi->cs_inactive &= ~BIT(device->chip_select);
	else
	spi->cs_inactive \|= BIT(device->chip_select);
	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, spi->cs_inactive);

	/* Select the correct device */
	sifive_spi_write(spi, SIFIVE_SPI_REG_CSID, device->chip_select);

	/* Set clock mode */
	sifive_spi_write(spi, SIFIVE_SPI_REG_SCKMODE,
	device->mode & SIFIVE_SPI_SCKMODE_MODE_MASK);

	return 0;
	}

	static void sifive_spi_set_cs(struct spi_device *device, bool is_high)
	{
	struct sifive_spi *spi = spi_master_get_devdata(device->master);

	/* Reverse polarity is handled by SCMR/CPOL. Not inverted CS. */
	if (device->mode & SPI_CS_HIGH)
	is_high = !is_high;

	sifive_spi_write(spi, SIFIVE_SPI_REG_CSMODE, is_high ?
	SIFIVE_SPI_CSMODE_MODE_AUTO :
	SIFIVE_SPI_CSMODE_MODE_HOLD);
	}

	static int
	sifive_spi_prep_transfer(struct sifive_spi spi, struct spi_device device,
	struct spi_transfer *t)
	{
	u32 cr;
	unsigned int mode;

	/* Calculate and program the clock rate */
	cr = DIV_ROUND_UP(clk_get_rate(spi->clk) >> 1, t->speed_hz) - 1;
	cr &= SIFIVE_SPI_SCKDIV_DIV_MASK;
	sifive_spi_write(spi, SIFIVE_SPI_REG_SCKDIV, cr);

	mode = max_t(unsigned int, t->rx_nbits, t->tx_nbits);

	/* Set frame format */
	cr = SIFIVE_SPI_FMT_LEN(t->bits_per_word);
	switch (mode) {
	case SPI_NBITS_QUAD:
	cr \|= SIFIVE_SPI_FMT_PROTO_QUAD;
	break;
	case SPI_NBITS_DUAL:
	cr \|= SIFIVE_SPI_FMT_PROTO_DUAL;
	break;
	default:
	cr \|= SIFIVE_SPI_FMT_PROTO_SINGLE;
	break;
	}
	if (device->mode & SPI_LSB_FIRST)
	cr \|= SIFIVE_SPI_FMT_ENDIAN;
	if (!t->rx_buf)
	cr \|= SIFIVE_SPI_FMT_DIR;
	sifive_spi_write(spi, SIFIVE_SPI_REG_FMT, cr);

	/* We will want to poll if the time we need to wait is
	* less than the context switching time.
	* Let's call that threshold 5us. The operation will take:
	* (8/mode) * fifo_depth / hz <= 5 * 10^-6
	* 1600000 * fifo_depth <= hz * mode
	*/
	return 1600000 * spi->fifo_depth <= t->speed_hz * mode;
	}

	static irqreturn_t sifive_spi_irq(int irq, void *dev_id)
	{
	struct sifive_spi *spi = dev_id;
	u32 ip = sifive_spi_read(spi, SIFIVE_SPI_REG_IP);

	if (ip & (SIFIVE_SPI_IP_TXWM \| SIFIVE_SPI_IP_RXWM)) {
	/* Disable interrupts until next transfer */
	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);
	complete(&spi->done);
	return IRQ_HANDLED;
	}

	return IRQ_NONE;
	}

	static void sifive_spi_wait(struct sifive_spi *spi, u32 bit, int poll)
	{
	if (poll) {
	u32 cr;

	do {
	cr = sifive_spi_read(spi, SIFIVE_SPI_REG_IP);
	} while (!(cr & bit));
	} else {
	reinit_completion(&spi->done);
	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, bit);
	wait_for_completion(&spi->done);
	}
	}

	static void sifive_spi_tx(struct sifive_spi spi, const u8 tx_ptr)
	{
	WARN_ON_ONCE((sifive_spi_read(spi, SIFIVE_SPI_REG_TXDATA)
	& SIFIVE_SPI_TXDATA_FULL) != 0);
	sifive_spi_write(spi, SIFIVE_SPI_REG_TXDATA,
	*tx_ptr & SIFIVE_SPI_TXDATA_DATA_MASK);
	}

	static void sifive_spi_rx(struct sifive_spi spi, u8 rx_ptr)
	{
	u32 data = sifive_spi_read(spi, SIFIVE_SPI_REG_RXDATA);

	WARN_ON_ONCE((data & SIFIVE_SPI_RXDATA_EMPTY) != 0);
	*rx_ptr = data & SIFIVE_SPI_RXDATA_DATA_MASK;
	}

	static int
	sifive_spi_transfer_one(struct spi_master master, struct spi_device device,
	struct spi_transfer *t)
	{
	struct sifive_spi *spi = spi_master_get_devdata(master);
	int poll = sifive_spi_prep_transfer(spi, device, t);
	const u8 *tx_ptr = t->tx_buf;
	u8 *rx_ptr = t->rx_buf;
	unsigned int remaining_words = t->len;

	while (remaining_words) {
	unsigned int n_words = min(remaining_words, spi->fifo_depth);
	unsigned int i;

	/* Enqueue n_words for transmission */
	for (i = 0; i < n_words; i++)
	sifive_spi_tx(spi, tx_ptr++);

	if (rx_ptr) {
	/* Wait for transmission + reception to complete */
	sifive_spi_write(spi, SIFIVE_SPI_REG_RXMARK,
	n_words - 1);
	sifive_spi_wait(spi, SIFIVE_SPI_IP_RXWM, poll);

	/* Read out all the data from the RX FIFO */
	for (i = 0; i < n_words; i++)
	sifive_spi_rx(spi, rx_ptr++);
	} else {
	/* Wait for transmission to complete */
	sifive_spi_wait(spi, SIFIVE_SPI_IP_TXWM, poll);
	}

	remaining_words -= n_words;
	}

	return 0;
	}

	static int sifive_spi_probe(struct platform_device *pdev)
	{
	struct sifive_spi *spi;
	int ret, irq, num_cs;
	u32 cs_bits, max_bits_per_word;
	struct spi_master *master;

	master = spi_alloc_master(&pdev->dev, sizeof(struct sifive_spi));
	if (!master) {
	dev_err(&pdev->dev, "out of memory\n");
	return -ENOMEM;
	}

	spi = spi_master_get_devdata(master);
	init_completion(&spi->done);
	platform_set_drvdata(pdev, master);

	spi->regs = devm_platform_ioremap_resource(pdev, 0);
	if (IS_ERR(spi->regs)) {
	ret = PTR_ERR(spi->regs);
	goto put_master;
	}

	spi->clk = devm_clk_get(&pdev->dev, NULL);
	if (IS_ERR(spi->clk)) {
	dev_err(&pdev->dev, "Unable to find bus clock\n");
	ret = PTR_ERR(spi->clk);
	goto put_master;
	}

	irq = platform_get_irq(pdev, 0);
	if (irq < 0) {
	ret = irq;
	goto put_master;
	}

	/* Optional parameters */
	ret =
	of_property_read_u32(pdev->dev.of_node, "sifive,fifo-depth",
	&spi->fifo_depth);
	if (ret < 0)
	spi->fifo_depth = SIFIVE_SPI_DEFAULT_DEPTH;

	ret =
	of_property_read_u32(pdev->dev.of_node, "sifive,max-bits-per-word",
	&max_bits_per_word);

	if (!ret && max_bits_per_word < 8) {
	dev_err(&pdev->dev, "Only 8bit SPI words supported by the driver\n");
	ret = -EINVAL;
	goto put_master;
	}

	/* Spin up the bus clock before hitting registers */
	ret = clk_prepare_enable(spi->clk);
	if (ret) {
	dev_err(&pdev->dev, "Unable to enable bus clock\n");
	goto put_master;
	}

	/* probe the number of CS lines */
	spi->cs_inactive = sifive_spi_read(spi, SIFIVE_SPI_REG_CSDEF);
	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, 0xffffffffU);
	cs_bits = sifive_spi_read(spi, SIFIVE_SPI_REG_CSDEF);
	sifive_spi_write(spi, SIFIVE_SPI_REG_CSDEF, spi->cs_inactive);
	if (!cs_bits) {
	dev_err(&pdev->dev, "Could not auto probe CS lines\n");
	ret = -EINVAL;
	goto disable_clk;
	}

	num_cs = ilog2(cs_bits) + 1;
	if (num_cs > SIFIVE_SPI_MAX_CS) {
	dev_err(&pdev->dev, "Invalid number of spi slaves\n");
	ret = -EINVAL;
	goto disable_clk;
	}

	/* Define our master */
	master->dev.of_node = pdev->dev.of_node;
	master->bus_num = pdev->id;
	master->num_chipselect = num_cs;
	master->mode_bits = SPI_CPHA \| SPI_CPOL
	\| SPI_CS_HIGH \| SPI_LSB_FIRST
	\| SPI_TX_DUAL \| SPI_TX_QUAD
	\| SPI_RX_DUAL \| SPI_RX_QUAD;
	/* TODO: add driver support for bits_per_word < 8
	* we need to "left-align" the bits (unless SPI_LSB_FIRST)
	*/
	master->bits_per_word_mask = SPI_BPW_MASK(8);
	master->flags = SPI_CONTROLLER_MUST_TX \| SPI_MASTER_GPIO_SS;
	master->prepare_message = sifive_spi_prepare_message;
	master->set_cs = sifive_spi_set_cs;
	master->transfer_one = sifive_spi_transfer_one;

	pdev->dev.dma_mask = NULL;
	/* Configure the SPI master hardware */
	sifive_spi_init(spi);

	/* Register for SPI Interrupt */
	ret = devm_request_irq(&pdev->dev, irq, sifive_spi_irq, 0,
	dev_name(&pdev->dev), spi);
	if (ret) {
	dev_err(&pdev->dev, "Unable to bind to interrupt\n");
	goto disable_clk;
	}

	dev_info(&pdev->dev, "mapped; irq=%d, cs=%d\n",
	irq, master->num_chipselect);

	ret = devm_spi_register_master(&pdev->dev, master);
	if (ret < 0) {
	dev_err(&pdev->dev, "spi_register_master failed\n");
	goto disable_clk;
	}

	return 0;

	disable_clk:
	clk_disable_unprepare(spi->clk);
	put_master:
	spi_master_put(master);

	return ret;
	}

	static int sifive_spi_remove(struct platform_device *pdev)
	{
	struct spi_master *master = platform_get_drvdata(pdev);
	struct sifive_spi *spi = spi_master_get_devdata(master);

	/* Disable all the interrupts just in case */
	sifive_spi_write(spi, SIFIVE_SPI_REG_IE, 0);
	clk_disable_unprepare(spi->clk);

	return 0;
	}

	static const struct of_device_id sifive_spi_of_match[] = {
	{ .compatible = "sifive,spi0", },
	{}
	};
	MODULE_DEVICE_TABLE(of, sifive_spi_of_match);

	static struct platform_driver sifive_spi_driver = {
	.probe = sifive_spi_probe,
	.remove = sifive_spi_remove,
	.driver = {
	.name = SIFIVE_SPI_DRIVER_NAME,
	.of_match_table = sifive_spi_of_match,
	},
	};
	module_platform_driver(sifive_spi_driver);

	MODULE_AUTHOR("SiFive, Inc. <sifive@sifive.com>");
	MODULE_DESCRIPTION("SiFive SPI driver");
	MODULE_LICENSE("GPL");