drivers/spi/tegra20_slink.c - github/trini/u-boot - Gitiles

 /*
  * NVIDIA Tegra SPI-SLINK controller
  *
  * Copyright (c) 2010-2013 NVIDIA Corporation
  *
  * See file CREDITS for list of people who contributed to this
  * project.
  *
  * This software is licensed under the terms of the GNU General Public
  * License version 2, as published by the Free Software Foundation, and
  * may be copied, distributed, and modified under those terms.
  *
  * 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., 59 Temple Place, Suite 330, Boston,
  * MA 02111-1307 USA
  */

 #include <common.h>
 #include <dm.h>
 #include <asm/io.h>
 #include <asm/arch/clock.h>
 #include <asm/arch-tegra/clk_rst.h>
 #include <spi.h>
 #include <fdtdec.h>
 #include "tegra_spi.h"

 DECLARE_GLOBAL_DATA_PTR;

 /* COMMAND */
 #define SLINK_CMD_ENB			(1 << 31)
 #define SLINK_CMD_GO			(1 << 30)
 #define SLINK_CMD_M_S			(1 << 28)
 #define SLINK_CMD_CK_SDA		(1 << 21)
 #define SLINK_CMD_CS_POL		(1 << 13)
 #define SLINK_CMD_CS_VAL		(1 << 12)
 #define SLINK_CMD_CS_SOFT		(1 << 11)
 #define SLINK_CMD_BIT_LENGTH		(1 << 4)
 #define SLINK_CMD_BIT_LENGTH_MASK	0x0000001F
 /* COMMAND2 */
 #define SLINK_CMD2_TXEN			(1 << 30)
 #define SLINK_CMD2_RXEN			(1 << 31)
 #define SLINK_CMD2_SS_EN		(1 << 18)
 #define SLINK_CMD2_SS_EN_SHIFT		18
 #define SLINK_CMD2_SS_EN_MASK		0x000C0000
 #define SLINK_CMD2_CS_ACTIVE_BETWEEN	(1 << 17)
 /* STATUS */
 #define SLINK_STAT_BSY			(1 << 31)
 #define SLINK_STAT_RDY			(1 << 30)
 #define SLINK_STAT_ERR			(1 << 29)
 #define SLINK_STAT_RXF_FLUSH		(1 << 27)
 #define SLINK_STAT_TXF_FLUSH		(1 << 26)
 #define SLINK_STAT_RXF_OVF		(1 << 25)
 #define SLINK_STAT_TXF_UNR		(1 << 24)
 #define SLINK_STAT_RXF_EMPTY		(1 << 23)
 #define SLINK_STAT_RXF_FULL		(1 << 22)
 #define SLINK_STAT_TXF_EMPTY		(1 << 21)
 #define SLINK_STAT_TXF_FULL		(1 << 20)
 #define SLINK_STAT_TXF_OVF		(1 << 19)
 #define SLINK_STAT_RXF_UNR		(1 << 18)
 #define SLINK_STAT_CUR_BLKCNT		(1 << 15)
 /* STATUS2 */
 #define SLINK_STAT2_RXF_FULL_CNT	(1 << 16)
 #define SLINK_STAT2_TXF_FULL_CNT	(1 << 0)

 #define SPI_TIMEOUT		1000
 #define TEGRA_SPI_MAX_FREQ	52000000

 struct spi_regs {
 	u32 command;	/* SLINK_COMMAND_0 register  */
 	u32 command2;	/* SLINK_COMMAND2_0 reg */
 	u32 status;	/* SLINK_STATUS_0 register */
 	u32 reserved;	/* Reserved offset 0C */
 	u32 mas_data;	/* SLINK_MAS_DATA_0 reg */
 	u32 slav_data;	/* SLINK_SLAVE_DATA_0 reg */
 	u32 dma_ctl;	/* SLINK_DMA_CTL_0 register */
 	u32 status2;	/* SLINK_STATUS2_0 reg */
 	u32 rsvd[56];	/* 0x20 to 0xFF reserved */
 	u32 tx_fifo;	/* SLINK_TX_FIFO_0 reg off 100h */
 	u32 rsvd2[31];	/* 0x104 to 0x17F reserved */
 	u32 rx_fifo;	/* SLINK_RX_FIFO_0 reg off 180h */
 };

 struct tegra30_spi_priv {
 	struct spi_regs *regs;
 	unsigned int freq;
 	unsigned int mode;
 	int periph_id;
 	int valid;
 	int last_transaction_us;
 };

 struct tegra_spi_slave {
 	struct spi_slave slave;
 	struct tegra30_spi_priv *ctrl;
 };

 static int tegra30_spi_ofdata_to_platdata(struct udevice *bus)
 {
 	struct tegra_spi_platdata *plat = bus->platdata;
 	const void *blob = gd->fdt_blob;
 	int node = bus->of_offset;

 	plat->base = fdtdec_get_addr(blob, node, "reg");
 	plat->periph_id = clock_decode_periph_id(blob, node);

 	if (plat->periph_id == PERIPH_ID_NONE) {
 		debug("%s: could not decode periph id %d\n", __func__,
 		      plat->periph_id);
 		return -FDT_ERR_NOTFOUND;
 	}

 	/* Use 500KHz as a suitable default */
 	plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency",
 					500000);
 	plat->deactivate_delay_us = fdtdec_get_int(blob, node,
 					"spi-deactivate-delay", 0);
 	debug("%s: base=%#08lx, periph_id=%d, max-frequency=%d, deactivate_delay=%d\n",
 	      __func__, plat->base, plat->periph_id, plat->frequency,
 	      plat->deactivate_delay_us);

 	return 0;
 }

 static int tegra30_spi_probe(struct udevice *bus)
 {
 	struct tegra_spi_platdata *plat = dev_get_platdata(bus);
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);

 	priv->regs = (struct spi_regs *)plat->base;

 	priv->last_transaction_us = timer_get_us();
 	priv->freq = plat->frequency;
 	priv->periph_id = plat->periph_id;

 	return 0;
 }

 static int tegra30_spi_claim_bus(struct udevice *bus)
 {
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);
 	struct spi_regs *regs = priv->regs;
 	u32 reg;

 	/* Change SPI clock to correct frequency, PLLP_OUT0 source */
 	clock_start_periph_pll(priv->periph_id, CLOCK_ID_PERIPH,
 			       priv->freq);

 	/* Clear stale status here */
 	reg = SLINK_STAT_RDY | SLINK_STAT_RXF_FLUSH | SLINK_STAT_TXF_FLUSH | \
 		SLINK_STAT_RXF_UNR | SLINK_STAT_TXF_OVF;
 	writel(reg, &regs->status);
 	debug("%s: STATUS = %08x\n", __func__, readl(&regs->status));

 	/* Set master mode and sw controlled CS */
 	reg = readl(&regs->command);
 	reg |= SLINK_CMD_M_S | SLINK_CMD_CS_SOFT;
 	writel(reg, &regs->command);
 	debug("%s: COMMAND = %08x\n", __func__, readl(&regs->command));

 	return 0;
 }

 static void spi_cs_activate(struct udevice *dev)
 {
 	struct udevice *bus = dev->parent;
 	struct tegra_spi_platdata *pdata = dev_get_platdata(bus);
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);

 	/* If it's too soon to do another transaction, wait */
 	if (pdata->deactivate_delay_us &&
 	    priv->last_transaction_us) {
 		ulong delay_us;		/* The delay completed so far */
 		delay_us = timer_get_us() - priv->last_transaction_us;
 		if (delay_us < pdata->deactivate_delay_us)
 			udelay(pdata->deactivate_delay_us - delay_us);
 	}

 	/* CS is negated on Tegra, so drive a 1 to get a 0 */
 	setbits_le32(&priv->regs->command, SLINK_CMD_CS_VAL);
 }

 static void spi_cs_deactivate(struct udevice *dev)
 {
 	struct udevice *bus = dev->parent;
 	struct tegra_spi_platdata *pdata = dev_get_platdata(bus);
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);

 	/* CS is negated on Tegra, so drive a 0 to get a 1 */
 	clrbits_le32(&priv->regs->command, SLINK_CMD_CS_VAL);

 	/* Remember time of this transaction so we can honour the bus delay */
 	if (pdata->deactivate_delay_us)
 		priv->last_transaction_us = timer_get_us();
 }

 static int tegra30_spi_xfer(struct udevice *dev, unsigned int bitlen,
 			    const void *data_out, void *data_in,
 			    unsigned long flags)
 {
 	struct udevice *bus = dev->parent;
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);
 	struct spi_regs *regs = priv->regs;
 	u32 reg, tmpdout, tmpdin = 0;
 	const u8 *dout = data_out;
 	u8 *din = data_in;
 	int num_bytes;
 	int ret;

 	debug("%s: slave %u:%u dout %p din %p bitlen %u\n",
 	      __func__, bus->seq, spi_chip_select(dev), dout, din, bitlen);
 	if (bitlen % 8)
 		return -1;
 	num_bytes = bitlen / 8;

 	ret = 0;

 	reg = readl(&regs->status);
 	writel(reg, &regs->status);	/* Clear all SPI events via R/W */
 	debug("%s entry: STATUS = %08x\n", __func__, reg);

 	reg = readl(&regs->status2);
 	writel(reg, &regs->status2);	/* Clear all STATUS2 events via R/W */
 	debug("%s entry: STATUS2 = %08x\n", __func__, reg);

 	debug("%s entry: COMMAND = %08x\n", __func__, readl(&regs->command));

 	clrsetbits_le32(&regs->command2, SLINK_CMD2_SS_EN_MASK,
 			SLINK_CMD2_TXEN | SLINK_CMD2_RXEN |
 			(spi_chip_select(dev) << SLINK_CMD2_SS_EN_SHIFT));
 	debug("%s entry: COMMAND2 = %08x\n", __func__, readl(&regs->command2));

 	if (flags & SPI_XFER_BEGIN)
 		spi_cs_activate(dev);

 	/* handle data in 32-bit chunks */
 	while (num_bytes > 0) {
 		int bytes;
 		int is_read = 0;
 		int tm, i;

 		tmpdout = 0;
 		bytes = (num_bytes > 4) ?  4 : num_bytes;

 		if (dout != NULL) {
 			for (i = 0; i < bytes; ++i)
 				tmpdout = (tmpdout << 8) | dout[i];
 			dout += bytes;
 		}

 		num_bytes -= bytes;

 		clrsetbits_le32(&regs->command, SLINK_CMD_BIT_LENGTH_MASK,
 				bytes * 8 - 1);
 		writel(tmpdout, &regs->tx_fifo);
 		setbits_le32(&regs->command, SLINK_CMD_GO);

 		/*
 		 * Wait for SPI transmit FIFO to empty, or to time out.
 		 * The RX FIFO status will be read and cleared last
 		 */
 		for (tm = 0, is_read = 0; tm < SPI_TIMEOUT; ++tm) {
 			u32 status;

 			status = readl(&regs->status);

 			/* We can exit when we've had both RX and TX activity */
 			if (is_read && (status & SLINK_STAT_TXF_EMPTY))
 				break;

 			if ((status & (SLINK_STAT_BSY | SLINK_STAT_RDY)) !=
 					SLINK_STAT_RDY)
 				tm++;

 			else if (!(status & SLINK_STAT_RXF_EMPTY)) {
 				tmpdin = readl(&regs->rx_fifo);
 				is_read = 1;

 				/* swap bytes read in */
 				if (din != NULL) {
 					for (i = bytes - 1; i >= 0; --i) {
 						din[i] = tmpdin & 0xff;
 						tmpdin >>= 8;
 					}
 					din += bytes;
 				}
 			}
 		}

 		if (tm >= SPI_TIMEOUT)
 			ret = tm;

 		/* clear ACK RDY, etc. bits */
 		writel(readl(&regs->status), &regs->status);
 	}

 	if (flags & SPI_XFER_END)
 		spi_cs_deactivate(dev);

 	debug("%s: transfer ended. Value=%08x, status = %08x\n",
 	      __func__, tmpdin, readl(&regs->status));

 	if (ret) {
 		printf("%s: timeout during SPI transfer, tm %d\n",
 		       __func__, ret);
 		return -1;
 	}

 	return 0;
 }

 static int tegra30_spi_set_speed(struct udevice *bus, uint speed)
 {
 	struct tegra_spi_platdata *plat = bus->platdata;
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);

 	if (speed > plat->frequency)
 		speed = plat->frequency;
 	priv->freq = speed;
 	debug("%s: regs=%p, speed=%d\n", __func__, priv->regs, priv->freq);

 	return 0;
 }

 static int tegra30_spi_set_mode(struct udevice *bus, uint mode)
 {
 	struct tegra30_spi_priv *priv = dev_get_priv(bus);

 	priv->mode = mode;
 	debug("%s: regs=%p, mode=%d\n", __func__, priv->regs, priv->mode);

 	return 0;
 }

 static const struct dm_spi_ops tegra30_spi_ops = {
 	.claim_bus	= tegra30_spi_claim_bus,
 	.xfer		= tegra30_spi_xfer,
 	.set_speed	= tegra30_spi_set_speed,
 	.set_mode	= tegra30_spi_set_mode,
 	/*
 	 * cs_info is not needed, since we require all chip selects to be
 	 * in the device tree explicitly
 	 */
 };

 static const struct udevice_id tegra30_spi_ids[] = {
 	{ .compatible = "nvidia,tegra20-slink" },
 	{ }
 };

 U_BOOT_DRIVER(tegra30_spi) = {
 	.name	= "tegra20_slink",
 	.id	= UCLASS_SPI,
 	.of_match = tegra30_spi_ids,
 	.ops	= &tegra30_spi_ops,
 	.ofdata_to_platdata = tegra30_spi_ofdata_to_platdata,
 	.platdata_auto_alloc_size = sizeof(struct tegra_spi_platdata),
 	.priv_auto_alloc_size = sizeof(struct tegra30_spi_priv),
 	.per_child_auto_alloc_size	= sizeof(struct spi_slave),
 	.probe	= tegra30_spi_probe,
 };
	/*
	* NVIDIA Tegra SPI-SLINK controller
	*
	* Copyright (c) 2010-2013 NVIDIA Corporation
	*
	* See file CREDITS for list of people who contributed to this
	* project.
	*
	* This software is licensed under the terms of the GNU General Public
	* License version 2, as published by the Free Software Foundation, and
	* may be copied, distributed, and modified under those terms.
	*
	* 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., 59 Temple Place, Suite 330, Boston,
	* MA 02111-1307 USA
	*/

	#include <common.h>
	#include <dm.h>
	#include <asm/io.h>
	#include <asm/arch/clock.h>
	#include <asm/arch-tegra/clk_rst.h>
	#include <spi.h>
	#include <fdtdec.h>
	#include "tegra_spi.h"

	DECLARE_GLOBAL_DATA_PTR;

	/* COMMAND */
	#define SLINK_CMD_ENB (1 << 31)
	#define SLINK_CMD_GO (1 << 30)
	#define SLINK_CMD_M_S (1 << 28)
	#define SLINK_CMD_CK_SDA (1 << 21)
	#define SLINK_CMD_CS_POL (1 << 13)
	#define SLINK_CMD_CS_VAL (1 << 12)
	#define SLINK_CMD_CS_SOFT (1 << 11)
	#define SLINK_CMD_BIT_LENGTH (1 << 4)
	#define SLINK_CMD_BIT_LENGTH_MASK 0x0000001F
	/* COMMAND2 */
	#define SLINK_CMD2_TXEN (1 << 30)
	#define SLINK_CMD2_RXEN (1 << 31)
	#define SLINK_CMD2_SS_EN (1 << 18)
	#define SLINK_CMD2_SS_EN_SHIFT 18
	#define SLINK_CMD2_SS_EN_MASK 0x000C0000
	#define SLINK_CMD2_CS_ACTIVE_BETWEEN (1 << 17)
	/* STATUS */
	#define SLINK_STAT_BSY (1 << 31)
	#define SLINK_STAT_RDY (1 << 30)
	#define SLINK_STAT_ERR (1 << 29)
	#define SLINK_STAT_RXF_FLUSH (1 << 27)
	#define SLINK_STAT_TXF_FLUSH (1 << 26)
	#define SLINK_STAT_RXF_OVF (1 << 25)
	#define SLINK_STAT_TXF_UNR (1 << 24)
	#define SLINK_STAT_RXF_EMPTY (1 << 23)
	#define SLINK_STAT_RXF_FULL (1 << 22)
	#define SLINK_STAT_TXF_EMPTY (1 << 21)
	#define SLINK_STAT_TXF_FULL (1 << 20)
	#define SLINK_STAT_TXF_OVF (1 << 19)
	#define SLINK_STAT_RXF_UNR (1 << 18)
	#define SLINK_STAT_CUR_BLKCNT (1 << 15)
	/* STATUS2 */
	#define SLINK_STAT2_RXF_FULL_CNT (1 << 16)
	#define SLINK_STAT2_TXF_FULL_CNT (1 << 0)

	#define SPI_TIMEOUT 1000
	#define TEGRA_SPI_MAX_FREQ 52000000

	struct spi_regs {
	u32 command; /* SLINK_COMMAND_0 register */
	u32 command2; /* SLINK_COMMAND2_0 reg */
	u32 status; /* SLINK_STATUS_0 register */
	u32 reserved; /* Reserved offset 0C */
	u32 mas_data; /* SLINK_MAS_DATA_0 reg */
	u32 slav_data; /* SLINK_SLAVE_DATA_0 reg */
	u32 dma_ctl; /* SLINK_DMA_CTL_0 register */
	u32 status2; /* SLINK_STATUS2_0 reg */
	u32 rsvd[56]; /* 0x20 to 0xFF reserved */
	u32 tx_fifo; /* SLINK_TX_FIFO_0 reg off 100h */
	u32 rsvd2[31]; /* 0x104 to 0x17F reserved */
	u32 rx_fifo; /* SLINK_RX_FIFO_0 reg off 180h */
	};

	struct tegra30_spi_priv {
	struct spi_regs *regs;
	unsigned int freq;
	unsigned int mode;
	int periph_id;
	int valid;
	int last_transaction_us;
	};

	struct tegra_spi_slave {
	struct spi_slave slave;
	struct tegra30_spi_priv *ctrl;
	};

	static int tegra30_spi_ofdata_to_platdata(struct udevice *bus)
	{
	struct tegra_spi_platdata *plat = bus->platdata;
	const void *blob = gd->fdt_blob;
	int node = bus->of_offset;

	plat->base = fdtdec_get_addr(blob, node, "reg");
	plat->periph_id = clock_decode_periph_id(blob, node);

	if (plat->periph_id == PERIPH_ID_NONE) {
	debug("%s: could not decode periph id %d\n", __func__,
	plat->periph_id);
	return -FDT_ERR_NOTFOUND;
	}

	/* Use 500KHz as a suitable default */
	plat->frequency = fdtdec_get_int(blob, node, "spi-max-frequency",
	500000);
	plat->deactivate_delay_us = fdtdec_get_int(blob, node,
	"spi-deactivate-delay", 0);
	debug("%s: base=%#08lx, periph_id=%d, max-frequency=%d, deactivate_delay=%d\n",
	__func__, plat->base, plat->periph_id, plat->frequency,
	plat->deactivate_delay_us);

	return 0;
	}

	static int tegra30_spi_probe(struct udevice *bus)
	{
	struct tegra_spi_platdata *plat = dev_get_platdata(bus);
	struct tegra30_spi_priv *priv = dev_get_priv(bus);

	priv->regs = (struct spi_regs *)plat->base;

	priv->last_transaction_us = timer_get_us();
	priv->freq = plat->frequency;
	priv->periph_id = plat->periph_id;

	return 0;
	}

	static int tegra30_spi_claim_bus(struct udevice *bus)
	{
	struct tegra30_spi_priv *priv = dev_get_priv(bus);
	struct spi_regs *regs = priv->regs;
	u32 reg;

	/* Change SPI clock to correct frequency, PLLP_OUT0 source */
	clock_start_periph_pll(priv->periph_id, CLOCK_ID_PERIPH,
	priv->freq);

	/* Clear stale status here */
	reg = SLINK_STAT_RDY \| SLINK_STAT_RXF_FLUSH \| SLINK_STAT_TXF_FLUSH \| \
	SLINK_STAT_RXF_UNR \| SLINK_STAT_TXF_OVF;
	writel(reg, &regs->status);
	debug("%s: STATUS = %08x\n", __func__, readl(&regs->status));

	/* Set master mode and sw controlled CS */
	reg = readl(&regs->command);
	reg \|= SLINK_CMD_M_S \| SLINK_CMD_CS_SOFT;
	writel(reg, &regs->command);
	debug("%s: COMMAND = %08x\n", __func__, readl(&regs->command));

	return 0;
	}

	static void spi_cs_activate(struct udevice *dev)
	{
	struct udevice *bus = dev->parent;
	struct tegra_spi_platdata *pdata = dev_get_platdata(bus);
	struct tegra30_spi_priv *priv = dev_get_priv(bus);

	/* If it's too soon to do another transaction, wait */
	if (pdata->deactivate_delay_us &&
	priv->last_transaction_us) {
	ulong delay_us; /* The delay completed so far */
	delay_us = timer_get_us() - priv->last_transaction_us;
	if (delay_us < pdata->deactivate_delay_us)
	udelay(pdata->deactivate_delay_us - delay_us);
	}

	/* CS is negated on Tegra, so drive a 1 to get a 0 */
	setbits_le32(&priv->regs->command, SLINK_CMD_CS_VAL);
	}

	static void spi_cs_deactivate(struct udevice *dev)
	{
	struct udevice *bus = dev->parent;
	struct tegra_spi_platdata *pdata = dev_get_platdata(bus);
	struct tegra30_spi_priv *priv = dev_get_priv(bus);

	/* CS is negated on Tegra, so drive a 0 to get a 1 */
	clrbits_le32(&priv->regs->command, SLINK_CMD_CS_VAL);

	/* Remember time of this transaction so we can honour the bus delay */
	if (pdata->deactivate_delay_us)
	priv->last_transaction_us = timer_get_us();
	}

	static int tegra30_spi_xfer(struct udevice *dev, unsigned int bitlen,
	const void data_out, void data_in,
	unsigned long flags)
	{
	struct udevice *bus = dev->parent;
	struct tegra30_spi_priv *priv = dev_get_priv(bus);
	struct spi_regs *regs = priv->regs;
	u32 reg, tmpdout, tmpdin = 0;
	const u8 *dout = data_out;
	u8 *din = data_in;
	int num_bytes;
	int ret;

	debug("%s: slave %u:%u dout %p din %p bitlen %u\n",
	__func__, bus->seq, spi_chip_select(dev), dout, din, bitlen);
	if (bitlen % 8)
	return -1;
	num_bytes = bitlen / 8;

	ret = 0;

	reg = readl(&regs->status);
	writel(reg, &regs->status); /* Clear all SPI events via R/W */
	debug("%s entry: STATUS = %08x\n", __func__, reg);

	reg = readl(&regs->status2);
	writel(reg, &regs->status2); /* Clear all STATUS2 events via R/W */
	debug("%s entry: STATUS2 = %08x\n", __func__, reg);

	debug("%s entry: COMMAND = %08x\n", __func__, readl(&regs->command));

	clrsetbits_le32(&regs->command2, SLINK_CMD2_SS_EN_MASK,
	SLINK_CMD2_TXEN \| SLINK_CMD2_RXEN \|
	(spi_chip_select(dev) << SLINK_CMD2_SS_EN_SHIFT));
	debug("%s entry: COMMAND2 = %08x\n", __func__, readl(&regs->command2));

	if (flags & SPI_XFER_BEGIN)
	spi_cs_activate(dev);

	/* handle data in 32-bit chunks */
	while (num_bytes > 0) {
	int bytes;
	int is_read = 0;
	int tm, i;

	tmpdout = 0;
	bytes = (num_bytes > 4) ? 4 : num_bytes;

	if (dout != NULL) {
	for (i = 0; i < bytes; ++i)
	tmpdout = (tmpdout << 8) \| dout[i];
	dout += bytes;
	}

	num_bytes -= bytes;

	clrsetbits_le32(&regs->command, SLINK_CMD_BIT_LENGTH_MASK,
	bytes * 8 - 1);
	writel(tmpdout, &regs->tx_fifo);
	setbits_le32(&regs->command, SLINK_CMD_GO);

	/*
	* Wait for SPI transmit FIFO to empty, or to time out.
	* The RX FIFO status will be read and cleared last
	*/
	for (tm = 0, is_read = 0; tm < SPI_TIMEOUT; ++tm) {
	u32 status;

	status = readl(&regs->status);

	/* We can exit when we've had both RX and TX activity */
	if (is_read && (status & SLINK_STAT_TXF_EMPTY))
	break;

	if ((status & (SLINK_STAT_BSY \| SLINK_STAT_RDY)) !=
	SLINK_STAT_RDY)
	tm++;

	else if (!(status & SLINK_STAT_RXF_EMPTY)) {
	tmpdin = readl(&regs->rx_fifo);
	is_read = 1;

	/* swap bytes read in */
	if (din != NULL) {
	for (i = bytes - 1; i >= 0; --i) {
	din[i] = tmpdin & 0xff;
	tmpdin >>= 8;
	}
	din += bytes;
	}
	}
	}

	if (tm >= SPI_TIMEOUT)
	ret = tm;

	/* clear ACK RDY, etc. bits */
	writel(readl(&regs->status), &regs->status);
	}

	if (flags & SPI_XFER_END)
	spi_cs_deactivate(dev);

	debug("%s: transfer ended. Value=%08x, status = %08x\n",
	__func__, tmpdin, readl(&regs->status));

	if (ret) {
	printf("%s: timeout during SPI transfer, tm %d\n",
	__func__, ret);
	return -1;
	}

	return 0;
	}

	static int tegra30_spi_set_speed(struct udevice *bus, uint speed)
	{
	struct tegra_spi_platdata *plat = bus->platdata;
	struct tegra30_spi_priv *priv = dev_get_priv(bus);

	if (speed > plat->frequency)
	speed = plat->frequency;
	priv->freq = speed;
	debug("%s: regs=%p, speed=%d\n", __func__, priv->regs, priv->freq);

	return 0;
	}

	static int tegra30_spi_set_mode(struct udevice *bus, uint mode)
	{
	struct tegra30_spi_priv *priv = dev_get_priv(bus);

	priv->mode = mode;
	debug("%s: regs=%p, mode=%d\n", __func__, priv->regs, priv->mode);

	return 0;
	}

	static const struct dm_spi_ops tegra30_spi_ops = {
	.claim_bus = tegra30_spi_claim_bus,
	.xfer = tegra30_spi_xfer,
	.set_speed = tegra30_spi_set_speed,
	.set_mode = tegra30_spi_set_mode,
	/*
	* cs_info is not needed, since we require all chip selects to be
	* in the device tree explicitly
	*/
	};

	static const struct udevice_id tegra30_spi_ids[] = {
	{ .compatible = "nvidia,tegra20-slink" },
	{ }
	};

	U_BOOT_DRIVER(tegra30_spi) = {
	.name = "tegra20_slink",
	.id = UCLASS_SPI,
	.of_match = tegra30_spi_ids,
	.ops = &tegra30_spi_ops,
	.ofdata_to_platdata = tegra30_spi_ofdata_to_platdata,
	.platdata_auto_alloc_size = sizeof(struct tegra_spi_platdata),
	.priv_auto_alloc_size = sizeof(struct tegra30_spi_priv),
	.per_child_auto_alloc_size = sizeof(struct spi_slave),
	.probe = tegra30_spi_probe,
	};