SPI API improvements

This patch gets rid of the spi_chipsel table and adds a handful of new
functions that makes the SPI layer cleaner and more flexible.

Instead of the spi_chipsel table, each board that wants to use SPI
gets to implement three hooks:
  * spi_cs_activate(): Activates the chipselect for a given slave
  * spi_cs_deactivate(): Deactivates the chipselect for a given slave
  * spi_cs_is_valid(): Determines if the given bus/chipselect
    combination can be activated.

Not all drivers may need those extra functions however. If that's the
case, the board code may just leave them out (assuming they know what
the driver needs) or rely on the linker to strip them out (assuming
--gc-sections is being used.)

To set up communication parameters for a given slave, the driver needs
to call spi_setup_slave(). This returns a pointer to an opaque
spi_slave struct which must be passed as a parameter to subsequent SPI
calls. This struct can be freed by calling spi_free_slave(), but most
driver probably don't want to do this.

Before starting one or more SPI transfers, the driver must call
spi_claim_bus() to gain exclusive access to the SPI bus and initialize
the hardware. When all transfers are done, the driver must call
spi_release_bus() to make the bus available to others, and possibly
shut down the SPI controller hardware.

spi_xfer() behaves mostly the same as before, but it now takes a
spi_slave parameter instead of a spi_chipsel function pointer. It also
got a new parameter, flags, which is used to specify chip select
behaviour. This may be extended with other flags in the future.

This patch has been build-tested on all powerpc and arm boards
involved. I have not tested NIOS since I don't have a toolchain for it
installed, so I expect some breakage there even though I've tried
fixing up everything I could find by visual inspection.

I have run-time tested this on AVR32 ATNGW100 using the atmel_spi and
DataFlash drivers posted as a follow-up. I'd like some help testing
other boards that use the existing SPI API.

But most of all, I'd like some comments on the new API. Is this stuff
usable for everyone? If not, why?

Changed in v4:
  - Build fixes for various boards, drivers and commands
  - Provide common struct spi_slave definition that can be extended by
    drivers
  - Pass a struct spi_slave * to spi_cs_activate and spi_cs_deactivate
  - Make default bus and mode build-time configurable
  - Override default SPI bus ID and mode on mx32ads and imx31_litekit.

Changed in v3:
  - Add opaque struct spi_slave for controller-specific data associated
    with a slave.
  - Add spi_claim_bus() and spi_release_bus()
  - Add spi_free_slave()
  - spi_setup() is now called spi_setup_slave() and returns a
    struct spi_slave
  - soft_spi now supports four SPI modes (CPOL|CPHA)
  - Add bus parameter to spi_setup_slave()
  - Convert the new i.MX32 SPI driver
  - Convert the new MC13783 RTC driver

Changed in v2:
  - Convert the mpc8xxx_spi driver and the mpc8349emds board to the
    new API.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>
Tested-by: Guennadi Liakhovetski <lg@denx.de>

board/amcc/taihu/taihu.c

@@ -165,16 +165,20 @@ unsigned char spi_read(void)
 	return (unsigned char)gpio_read_in_bit(SPI_DIN_GPIO15);
 }
 
-void taihu_spi_chipsel(int cs)
+int spi_cs_is_valid(unsigned int bus, unsigned int cs)
 {
-	gpio_write_bit(SPI_CS_GPIO0, cs);
+	return bus == 0 && cs == 0;
 }
 
-spi_chipsel_type spi_chipsel[]= {
-	taihu_spi_chipsel
-};
+void spi_cs_activate(struct spi_slave *slave)
+{
+	gpio_write_bit(SPI_CS_GPIO0, 1);
+}
 
-int spi_chipsel_cnt = sizeof(spi_chipsel) / sizeof(spi_chipsel[0]);
+void spi_cs_deactivate(struct spi_slave *slave)
+{
+	gpio_write_bit(SPI_CS_GPIO0, 0);
+}
 
 #ifdef CONFIG_PCI
 static unsigned char int_lines[32] = {

board/freescale/mpc8349emds/mpc8349emds.c

@@ -257,25 +257,24 @@ void sdram_init(void)
 
 #define SPI_CS_MASK	0x80000000
 
-void spi_eeprom_chipsel(int cs)
+int spi_cs_is_valid(unsigned int bus, unsigned int cs)
+{
+	return bus == 0 && cs == 0;
+}
+
+void spi_cs_activate(struct spi_slave *slave)
 {
 	volatile gpio83xx_t *iopd = &((immap_t *)CFG_IMMR)->gpio[0];
 
-	if (cs)
-		iopd->dat &= ~SPI_CS_MASK;
-	else
-		iopd->dat |=  SPI_CS_MASK;
+	iopd->dat &= ~SPI_CS_MASK;
 }
 
-/*
- * The SPI command uses this table of functions for controlling the SPI
- * chip selects.
- */
-spi_chipsel_type spi_chipsel[] = {
-	spi_eeprom_chipsel,
-};
-int spi_chipsel_cnt = sizeof(spi_chipsel) / sizeof(spi_chipsel[0]);
+void spi_cs_deactivate(struct spi_slave *slave)
+{
+	volatile gpio83xx_t *iopd = &((immap_t *)CFG_IMMR)->gpio[0];
 
+	iopd->dat |=  SPI_CS_MASK;
+}
 #endif /* CONFIG_HARD_SPI */
 
 #if defined(CONFIG_OF_BOARD_SETUP)

board/sacsng/sacsng.c

@@ -842,37 +842,30 @@ void show_boot_progress (int status)
 #define SPI_ADC_CS_MASK	0x00000800
 #define SPI_DAC_CS_MASK	0x00001000
 
-void spi_adc_chipsel(int cs)
+static const u32 cs_mask[] = {
+    SPI_ADC_CS_MASK,
+    SPI_DAC_CS_MASK,
+};
+
+int spi_cs_is_valid(unsigned int bus, unsigned int cs)
+{
+    return bus == 0 && cs < sizeof(cs_mask) / sizeof(cs_mask[0]);
+}
+
+void spi_cs_activate(struct spi_slave *slave)
 {
     volatile ioport_t *iopd = ioport_addr((immap_t *)CFG_IMMR, 3 /* port D */);
 
-    if(cs)
-	iopd->pdat &= ~SPI_ADC_CS_MASK;	/* activate the chip select */
-    else
-	iopd->pdat |=  SPI_ADC_CS_MASK;	/* deactivate the chip select */
+    iopd->pdat &= ~cs_mask[slave->cs];
 }
 
-void spi_dac_chipsel(int cs)
+void spi_cs_deactivate(struct spi_slave *slave)
 {
     volatile ioport_t *iopd = ioport_addr((immap_t *)CFG_IMMR, 3 /* port D */);
 
-    if(cs)
-	iopd->pdat &= ~SPI_DAC_CS_MASK;	/* activate the chip select */
-    else
-	iopd->pdat |=  SPI_DAC_CS_MASK;	/* deactivate the chip select */
+    iopd->pdat |= cs_mask[slave->cs];
 }
 
-/*
- * The SPI command uses this table of functions for controlling the SPI
- * chip selects: it calls the appropriate function to control the SPI
- * chip selects.
- */
-spi_chipsel_type spi_chipsel[] = {
-	spi_adc_chipsel,
-	spi_dac_chipsel
-};
-int spi_chipsel_cnt = sizeof(spi_chipsel) / sizeof(spi_chipsel[0]);
-
 #endif
 
 #endif /* CONFIG_MISC_INIT_R */

board/ssv/adnpesc1/adnpesc1.c

@@ -69,25 +69,24 @@ long int initdram (int board_type)
 
 #define	SPI_RTC_CS_MASK	0x00000001
 
-void spi_rtc_chipsel(int cs)
+int spi_cs_is_valid(unsigned int bus, unsigned int cs)
+{
+	return bus == 0 && cs == 0;
+}
+
+void spi_cs_activate(struct spi_slave *slave)
 {
 	nios_spi_t *spi = (nios_spi_t *)CFG_NIOS_SPIBASE;
 
-	if (cs)
-		spi->slaveselect = SPI_RTC_CS_MASK;	/* activate (1) */
-	else
-		spi->slaveselect = 0;			/* deactivate (0) */
+	spi->slaveselect = SPI_RTC_CS_MASK;	/* activate (1) */
 }
 
-/*
- * The SPI command uses this table of functions for controlling the SPI
- * chip selects: it calls the appropriate function to control the SPI
- * chip selects.
- */
-spi_chipsel_type spi_chipsel[] = {
-	spi_rtc_chipsel
-};
-int spi_chipsel_cnt = sizeof(spi_chipsel) / sizeof(spi_chipsel[0]);
+void spi_cs_deactivate(struct spi_slave *slave)
+{
+	nios_spi_t *spi = (nios_spi_t *)CFG_NIOS_SPIBASE;
+
+	spi->slaveselect = 0;			/* deactivate (0) */
+}
 
 #endif
 

common/cmd_df.c

@@ -0,0 +1,37 @@
+/*
+ * Command for accessing DataFlash.
+ *
+ * Copyright (C) 2008 Atmel Corporation
+ */
+#include <common.h>
+#include <df.h>
+
+static int do_df(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
+{
+	const char *cmd;
+
+	/* need at least two arguments */
+	if (argc < 2)
+		goto usage;
+
+	cmd = argv[1];
+
+	if (strcmp(cmd, "init") == 0) {
+		df_init(0, 0, 1000000);
+		return 0;
+	}
+
+	if (strcmp(cmd, "info") == 0) {
+		df_show_info();
+		return 0;
+	}
+
+usage:
+	printf("Usage:\n%s\n", cmdtp->usage);
+	return 1;
+}
+
+U_BOOT_CMD(
+	sf,	2,	1,	do_serial_flash,
+	"sf	- Serial flash sub-system\n",
+	"probe [bus:]cs		- init flash device on given SPI bus and CS\n")

common/cmd_spi.c

@@ -37,20 +37,20 @@
 #   define MAX_SPI_BYTES 32	/* Maximum number of bytes we can handle */
 #endif
 
-/*
- * External table of chip select functions (see the appropriate board
- * support for the actual definition of the table).
- */
-extern spi_chipsel_type spi_chipsel[];
-extern int spi_chipsel_cnt;
+#ifndef CONFIG_DEFAULT_SPI_BUS
+#   define CONFIG_DEFAULT_SPI_BUS	0
+#endif
+#ifndef CONFIG_DEFAULT_SPI_MODE
+#   define CONFIG_DEFAULT_SPI_MODE	SPI_MODE_0
+#endif
 
 /*
  * Values from last command.
  */
-static int   device;
-static int   bitlen;
-static uchar dout[MAX_SPI_BYTES];
-static uchar din[MAX_SPI_BYTES];
+static unsigned int	device;
+static int   		bitlen;
+static uchar 		dout[MAX_SPI_BYTES];
+static uchar 		din[MAX_SPI_BYTES];
 
 /*
  * SPI read/write
@@ -65,6 +65,7 @@ static uchar din[MAX_SPI_BYTES];
 
 int do_spi (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 {
+	struct spi_slave *slave;
 	char  *cp = 0;
 	uchar tmp;
 	int   j;
@@ -101,19 +102,24 @@ int do_spi (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 		}
 	}
 
-	if ((device < 0) || (device >=  spi_chipsel_cnt)) {
-		printf("Invalid device %d, giving up.\n", device);
-		return 1;
-	}
 	if ((bitlen < 0) || (bitlen >  (MAX_SPI_BYTES * 8))) {
 		printf("Invalid bitlen %d, giving up.\n", bitlen);
 		return 1;
 	}
 
-	debug ("spi_chipsel[%d] = %08X\n",
-		device, (uint)spi_chipsel[device]);
+	/* FIXME: Make these parameters run-time configurable */
+	slave = spi_setup_slave(CONFIG_DEFAULT_SPI_BUS, device, 1000000,
+			CONFIG_DEFAULT_SPI_MODE);
+	if (!slave) {
+		printf("Invalid device %d, giving up.\n", device);
+		return 1;
+	}
+
+	debug ("spi chipsel = %08X\n", device);
 
-	if(spi_xfer(spi_chipsel[device], bitlen, dout, din) != 0) {
+	spi_claim_bus(slave);
+	if(spi_xfer(slave, bitlen, dout, din,
+				SPI_XFER_BEGIN | SPI_XFER_END) != 0) {
 		printf("Error with the SPI transaction.\n");
 		rcode = 1;
 	} else {
@@ -123,6 +129,8 @@ int do_spi (cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
 		}
 		printf("\n");
 	}
+	spi_release_bus(slave);
+	spi_free_slave(slave);
 
 	return rcode;
 }

common/soft_spi.c

@@ -29,6 +29,8 @@
 
 #if defined(CONFIG_SOFT_SPI)
 
+#include <malloc.h>
+
 /*-----------------------------------------------------------------------
  * Definitions
  */
@@ -39,6 +41,15 @@
 #define PRINTD(fmt,args...)
 #endif
 
+struct soft_spi_slave {
+	struct spi_slave slave;
+	unsigned int mode;
+};
+
+static inline struct soft_spi_slave *to_soft_spi(struct spi_slave *slave)
+{
+	return container_of(slave, struct soft_spi_slave, slave);
+}
 
 /*=====================================================================*/
 /*                         Public Functions                            */
@@ -56,6 +67,57 @@ void spi_init (void)
 #endif
 }
 
+struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
+		unsigned int max_hz, unsigned int mode)
+{
+	struct soft_spi_slave *ss;
+
+	if (!spi_cs_is_valid(bus, cs))
+		return NULL;
+
+	ss = malloc(sizeof(struct soft_spi_slave));
+	if (!ss)
+		return NULL;
+
+	ss->slave.bus = bus;
+	ss->slave.cs = cs;
+	ss->mode = mode;
+
+	/* TODO: Use max_hz to limit the SCK rate */
+
+	return &ss->slave;
+}
+
+void spi_free_slave(struct spi_slave *slave)
+{
+	struct soft_spi_slave *ss = to_soft_spi(slave);
+
+	free(ss);
+}
+
+int spi_claim_bus(struct spi_slave *slave)
+{
+#ifdef CFG_IMMR
+	volatile immap_t *immr = (immap_t *)CFG_IMMR;
+#endif
+	struct soft_spi_slave *ss = to_soft_spi(slave);
+
+	/*
+	 * Make sure the SPI clock is in idle state as defined for
+	 * this slave.
+	 */
+	if (ss->mode & SPI_CPOL)
+		SPI_SCL(1);
+	else
+		SPI_SCL(0);
+
+	return 0;
+}
+
+void spi_release_bus(struct spi_slave *slave)
+{
+	/* Nothing to do */
+}
 
 /*-----------------------------------------------------------------------
  * SPI transfer
@@ -68,50 +130,54 @@ void spi_init (void)
  * and "din" can point to the same memory location, in which case the
  * input data overwrites the output data (since both are buffered by
  * temporary variables, this is OK).
- *
- * If the chipsel() function is not NULL, it is called with a parameter
- * of '1' (chip select active) at the start of the transfer and again with
- * a parameter of '0' at the end of the transfer.
- *
- * If the chipsel() function _is_ NULL, it the responsibility of the
- * caller to make the appropriate chip select active before calling
- * spi_xfer() and making it inactive after spi_xfer() returns.
  */
-int  spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
+int  spi_xfer(struct spi_slave *slave, unsigned int bitlen,
+		const void *dout, void *din, unsigned long flags)
 {
 #ifdef CFG_IMMR
 	volatile immap_t *immr = (immap_t *)CFG_IMMR;
 #endif
-	uchar tmpdin  = 0;
-	uchar tmpdout = 0;
-	int   j;
+	struct soft_spi_slave *ss = to_soft_spi(slave);
+	uchar		tmpdin  = 0;
+	uchar		tmpdout = 0;
+	const u8	*txd = dout;
+	u8		*rxd = din;
+	int		cpol = ss->mode & SPI_CPOL;
+	int		cpha = ss->mode & SPI_CPHA;
+	unsigned int	j;
 
-	PRINTD("spi_xfer: chipsel %08X dout %08X din %08X bitlen %d\n",
-		(int)chipsel, *(uint *)dout, *(uint *)din, bitlen);
+	PRINTD("spi_xfer: slave %u:%u dout %08X din %08X bitlen %u\n",
+		slave->bus, slave->cs, *(uint *)txd, *(uint *)rxd, bitlen);
 
-	if(chipsel != NULL) {
-		(*chipsel)(1);	/* select the target chip */
-	}
+	if (flags & SPI_XFER_BEGIN)
+		spi_cs_activate(slave);
 
 	for(j = 0; j < bitlen; j++) {
 		/*
 		 * Check if it is time to work on a new byte.
 		 */
 		if((j % 8) == 0) {
-			tmpdout = *dout++;
+			tmpdout = *txd++;
 			if(j != 0) {
-				*din++ = tmpdin;
+				*rxd++ = tmpdin;
 			}
 			tmpdin  = 0;
 		}
-		SPI_SCL(0);
+
+		if (!cpha)
+			SPI_SCL(!cpol);
 		SPI_SDA(tmpdout & 0x80);
 		SPI_DELAY;
-		SPI_SCL(1);
+		if (cpha)
+			SPI_SCL(!cpol);
+		else
+			SPI_SCL(cpol);
+		tmpdin	<<= 1;
+		tmpdin	|= SPI_READ;
+		tmpdout	<<= 1;
 		SPI_DELAY;
-		tmpdin  <<= 1;
-		tmpdin   |= SPI_READ;
-		tmpdout <<= 1;
+		if (cpha)
+			SPI_SCL(cpol);
 	}
 	/*
 	 * If the number of bits isn't a multiple of 8, shift the last
@@ -120,14 +186,10 @@ int  spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 	 */
 	if((bitlen % 8) != 0)
 		tmpdin <<= 8 - (bitlen % 8);
-	*din++ = tmpdin;
-
-	SPI_SCL(0);		/* SPI wants the clock left low for idle */
+	*rxd++ = tmpdin;
 
-	if(chipsel != NULL) {
-		(*chipsel)(0);	/* deselect the target chip */
-
-	}
+	if (flags & SPI_XFER_END)
+		spi_cs_deactivate(slave);
 
 	return(0);
 }

cpu/nios/spi.c

@@ -63,10 +63,10 @@ static char quickhex (int i)
 	return hex_digit[i];
 }
 
-static void memdump (void *pv, int num)
+static void memdump (const void *pv, int num)
 {
 	int i;
-	unsigned char *pc = (unsigned char *) pv;
+	const unsigned char *pc = (const unsigned char *) pv;
 
 	for (i = 0; i < num; i++)
 		printf ("%c%c ", quickhex (pc[i] >> 4), quickhex (pc[i] & 0x0f));
@@ -83,26 +83,64 @@ static void memdump (void *pv, int num)
 #endif  /* DEBUG */
 
 
+struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
+		unsigned int max_hz, unsigned int mode)
+{
+	struct spi_slave *slave;
+
+	if (!spi_cs_is_valid(bus, cs))
+		return NULL;
+
+	slave = malloc(sizeof(struct spi_slave));
+	if (!slave)
+		return NULL;
+
+	slave->bus = bus;
+	slave->cs = cs;
+
+	/* TODO: Add support for different modes and speeds */
+
+	return slave;
+}
+
+void spi_free_slave(struct spi_slave *slave)
+{
+	free(slave);
+}
+
+int spi_claim_bus(struct spi_slave *slave)
+{
+	return 0;
+}
+
+void spi_release_bus(struct spi_slave *slave)
+{
+
+}
+
 /*
  * SPI transfer:
  *
  * See include/spi.h and http://www.altera.com/literature/ds/ds_nios_spi.pdf
  * for more informations.
  */
-int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
+int spi_xfer(struct spi_slave *slave, int bitlen, const void *dout,
+		void *din, unsigned long flags)
 {
+	const u8 *txd = dout;
+	u8 *rxd = din;
 	int j;
 
-	DPRINT(("spi_xfer: chipsel %08X dout %08X din %08X bitlen %d\n",
-		(int)chipsel, *(uint *)dout, *(uint *)din, bitlen));
+	DPRINT(("spi_xfer: slave %u:%u dout %08X din %08X bitlen %d\n",
+		slave->bus, slave->cs, *(uint *)dout, *(uint *)din, bitlen));
 
-	memdump((void*)dout, (bitlen + 7) / 8);
+	memdump(dout, (bitlen + 7) / 8);
 
-	if(chipsel != NULL) {
-		chipsel(1);	/* select the target chip */
-	}
+	if (flags & SPI_XFER_BEGIN)
+		spi_cs_activate(slave);
 
-	if (bitlen > CFG_NIOS_SPIBITS) {	/* leave chip select active */
+	if (!(flags & SPI_XFER_END) || bitlen > CFG_NIOS_SPIBITS) {
+		/* leave chip select active */
 		spi->control |= NIOS_SPI_SSO;
 	}
 
@@ -114,11 +152,11 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 
 		while ((spi->status & NIOS_SPI_TRDY) == 0)
 			;
-		spi->txdata = (unsigned)(dout[j]);
+		spi->txdata = (unsigned)(txd[j]);
 
 		while ((spi->status & NIOS_SPI_RRDY) == 0)
 			;
-		din[j] = (unsigned char)(spi->rxdata & 0xff);
+		rxd[j] = (unsigned char)(spi->rxdata & 0xff);
 
 #elif	(CFG_NIOS_SPIBITS == 16)
 		j++, j++) {
@@ -126,15 +164,15 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 		while ((spi->status & NIOS_SPI_TRDY) == 0)
 			;
 		if ((j+1) < ((bitlen + 7) / 8))
-			spi->txdata = (unsigned)((dout[j] << 8) | dout[j+1]);
+			spi->txdata = (unsigned)((txd[j] << 8) | txd[j+1]);
 		else
-			spi->txdata = (unsigned)(dout[j] << 8);
+			spi->txdata = (unsigned)(txd[j] << 8);
 
 		while ((spi->status & NIOS_SPI_RRDY) == 0)
 			;
-		din[j] = (unsigned char)((spi->rxdata >> 8) & 0xff);
+		rxd[j] = (unsigned char)((spi->rxdata >> 8) & 0xff);
 		if ((j+1) < ((bitlen + 7) / 8))
-			din[j+1] = (unsigned char)(spi->rxdata & 0xff);
+			rxd[j+1] = (unsigned char)(spi->rxdata & 0xff);
 
 #else
 #error "*** unsupported value of CFG_NIOS_SPIBITS ***"
@@ -142,15 +180,14 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 
 	}
 
-	if (bitlen > CFG_NIOS_SPIBITS) {
+	if (bitlen > CFG_NIOS_SPIBITS && (flags & SPI_XFER_END)) {
 		spi->control &= ~NIOS_SPI_SSO;
 	}
 
-	if(chipsel != NULL) {
-		chipsel(0);	/* deselect the target chip */
-	}
+	if (flags & SPI_XFER_END)
+		spi_cs_deactivate(slave);
 
-	memdump((void*)din, (bitlen + 7) / 8);
+	memdump(din, (bitlen + 7) / 8);
 
 	return 0;
 }

drivers/rtc/ds1306.c

@@ -62,13 +62,6 @@
 
 #define	RTC_USER_RAM_BASE	0x20
 
-/*
- * External table of chip select functions (see the appropriate board
- * support for the actual definition of the table).
- */
-extern spi_chipsel_type spi_chipsel[];
-extern int spi_chipsel_cnt;
-
 static unsigned int bin2bcd (unsigned int n);
 static unsigned char bcd2bin (unsigned char c);
 
@@ -305,11 +298,29 @@ void rtc_reset (void)
 static unsigned char rtc_read (unsigned char reg);
 static void rtc_write (unsigned char reg, unsigned char val);
 
+static struct spi_slave *slave;
+
 /* read clock time from DS1306 and return it in *tmp */
 int rtc_get (struct rtc_time *tmp)
 {
 	unsigned char sec, min, hour, mday, wday, mon, year;
 
+	/*
+	 * Assuming Vcc = 2.0V (lowest speed)
+	 *
+	 * REVISIT: If we add an rtc_init() function we can do this
+	 * step just once.
+	 */
+	if (!slave) {
+		slave = spi_setup_slave(0, CFG_SPI_RTC_DEVID, 600000,
+				SPI_MODE_3 | SPI_CS_HIGH);
+		if (!slave)
+			return;
+	}
+
+	if (spi_claim_bus(slave))
+		return;
+
 	sec = rtc_read (RTC_SECONDS);
 	min = rtc_read (RTC_MINUTES);
 	hour = rtc_read (RTC_HOURS);
@@ -318,6 +329,8 @@ int rtc_get (struct rtc_time *tmp)
 	mon = rtc_read (RTC_MONTH);
 	year = rtc_read (RTC_YEAR);
 
+	spi_release_bus(slave);
+
 	debug ("Get RTC year: %02x mon: %02x mday: %02x wday: %02x "
 	       "hr: %02x min: %02x sec: %02x\n",
 	       year, mon, mday, wday, hour, min, sec);
@@ -360,6 +373,17 @@ int rtc_get (struct rtc_time *tmp)
 /* set clock time from *tmp in DS1306 RTC */
 void rtc_set (struct rtc_time *tmp)
 {
+	/* Assuming Vcc = 2.0V (lowest speed) */
+	if (!slave) {
+		slave = spi_setup_slave(0, CFG_SPI_RTC_DEVID, 600000,
+				SPI_MODE_3 | SPI_CS_HIGH);
+		if (!slave)
+			return;
+	}
+
+	if (spi_claim_bus(slave))
+		return;
+
 	debug ("Set DATE: %4d-%02d-%02d (wday=%d)  TIME: %2d:%02d:%02d\n",
 	       tmp->tm_year, tmp->tm_mon, tmp->tm_mday, tmp->tm_wday,
 	       tmp->tm_hour, tmp->tm_min, tmp->tm_sec);
@@ -371,6 +395,8 @@ void rtc_set (struct rtc_time *tmp)
 	rtc_write (RTC_DATE_OF_MONTH, bin2bcd (tmp->tm_mday));
 	rtc_write (RTC_MONTH, bin2bcd (tmp->tm_mon));
 	rtc_write (RTC_YEAR, bin2bcd (tmp->tm_year - 2000));
+
+	spi_release_bus(slave);
 }
 
 /* ------------------------------------------------------------------------- */
@@ -378,6 +404,17 @@ void rtc_set (struct rtc_time *tmp)
 /* reset the DS1306 */
 void rtc_reset (void)
 {
+	/* Assuming Vcc = 2.0V (lowest speed) */
+	if (!slave) {
+		slave = spi_setup_slave(0, CFG_SPI_RTC_DEVID, 600000,
+				SPI_MODE_3 | SPI_CS_HIGH);
+		if (!slave)
+			return;
+	}
+
+	if (spi_claim_bus(slave))
+		return;
+
 	/* clear the control register */
 	rtc_write (RTC_CONTROL, 0x00);	/* 1st step: reset WP */
 	rtc_write (RTC_CONTROL, 0x00);	/* 2nd step: reset 1Hz, AIE1, AIE0 */
@@ -391,22 +428,18 @@ void rtc_reset (void)
 	rtc_write (RTC_HOURS_ALARM1, 0x00);
 	rtc_write (RTC_DAY_OF_WEEK_ALARM0, 0x00);
 	rtc_write (RTC_DAY_OF_WEEK_ALARM1, 0x00);
+
+	spi_release_bus(slave);
 }
 
 /* ------------------------------------------------------------------------- */
 
 static unsigned char rtc_read (unsigned char reg)
 {
-	unsigned char dout[2];	/* SPI Output Data Bytes */
-	unsigned char din[2];	/* SPI Input Data Bytes */
-
-	dout[0] = reg;
+	int ret;
 
-	if (spi_xfer (spi_chipsel[CFG_SPI_RTC_DEVID], 16, dout, din) != 0) {
-		return 0;
-	} else {
-		return din[1];
-	}
+	ret = spi_w8r8(slave, reg);
+	return ret < 0 ? 0 : ret;
 }
 
 /* ------------------------------------------------------------------------- */
@@ -419,7 +452,7 @@ static void rtc_write (unsigned char reg, unsigned char val)
 	dout[0] = 0x80 | reg;
 	dout[1] = val;
 
-	spi_xfer (spi_chipsel[CFG_SPI_RTC_DEVID], 16, dout, din);
+	spi_xfer (slave, 16, dout, din, SPI_XFER_BEGIN | SPI_XFER_END);
 }
 
 #endif /* end of code exclusion (see #ifdef CONFIG_SXNI855T above) */

drivers/rtc/mc13783-rtc.c

@@ -24,34 +24,50 @@
 #include <rtc.h>
 #include <spi.h>
 
+static struct spi_slave *slave;
+
 int rtc_get(struct rtc_time *rtc)
 {
 	u32 day1, day2, time;
 	u32 reg;
 	int err, tim, i = 0;
 
-	spi_select(1, 0, SPI_MODE_2 | SPI_CS_HIGH);
+	if (!slave) {
+		/* FIXME: Verify the max SCK rate */
+		slave = spi_setup_slave(1, 0, 1000000,
+				SPI_MODE_2 | SPI_CS_HIGH);
+		if (!slave)
+			return -1;
+	}
+
+	if (spi_claim_bus(slave))
+		return -1;
 
 	do {
 		reg = 0x2c000000;
-		err = spi_xfer(0, 32, (uchar *)&reg, (uchar *)&day1);
+		err = spi_xfer(slave, 32, (uchar *)&reg, (uchar *)&day1,
+				SPI_XFER_BEGIN | SPI_XFER_END);
 
 		if (err)
 			return err;
 
 		reg = 0x28000000;
-		err = spi_xfer(0, 32, (uchar *)&reg, (uchar *)&time);
+		err = spi_xfer(slave, 32, (uchar *)&reg, (uchar *)&time,
+				SPI_XFER_BEGIN | SPI_XFER_END);
 
 		if (err)
 			return err;
 
 		reg = 0x2c000000;
-		err = spi_xfer(0, 32, (uchar *)&reg, (uchar *)&day2);
+		err = spi_xfer(slave, 32, (uchar *)&reg, (uchar *)&day2,
+				SPI_XFER_BEGIN | SPI_XFER_END);
 
 		if (err)
 			return err;
 	} while (day1 != day2 && i++ < 3);
 
+	spi_release_bus(slave);
+
 	tim = day1 * 86400 + time;
 	to_tm(tim, rtc);
 
@@ -65,16 +81,31 @@ void rtc_set(struct rtc_time *rtc)
 {
 	u32 time, day, reg;
 
+	if (!slave) {
+		/* FIXME: Verify the max SCK rate */
+		slave = spi_setup_slave(1, 0, 1000000,
+				SPI_MODE_2 | SPI_CS_HIGH);
+		if (!slave)
+			return;
+	}
+
 	time = mktime(rtc->tm_year, rtc->tm_mon, rtc->tm_mday,
 		      rtc->tm_hour, rtc->tm_min, rtc->tm_sec);
 	day = time / 86400;
 	time %= 86400;
 
+	if (spi_claim_bus(slave))
+		return;
+
 	reg = 0x2c000000 | day | 0x80000000;
-	spi_xfer(0, 32, (uchar *)&reg, (uchar *)&day);
+	spi_xfer(slave, 32, (uchar *)&reg, (uchar *)&day,
+			SPI_XFER_BEGIN | SPI_XFER_END);
 
 	reg = 0x28000000 | time | 0x80000000;
-	spi_xfer(0, 32, (uchar *)&reg, (uchar *)&time);
+	spi_xfer(slave, 32, (uchar *)&reg, (uchar *)&time,
+			SPI_XFER_BEGIN | SPI_XFER_END);
+
+	spi_release_bus(slave);
 }
 
 void rtc_reset(void)

drivers/spi/mpc8xxx_spi.c

@@ -24,6 +24,7 @@
 #include <common.h>
 #if defined(CONFIG_MPC8XXX_SPI) && defined(CONFIG_HARD_SPI)
 
+#include <malloc.h>
 #include <spi.h>
 #include <asm/mpc8xxx_spi.h>
 
@@ -37,6 +38,34 @@
 
 #define SPI_TIMEOUT	1000
 
+struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
+		unsigned int max_hz, unsigned int mode)
+{
+	struct spi_slave *slave;
+
+	if (!spi_cs_is_valid(bus, cs))
+		return NULL;
+
+	slave = malloc(sizeof(struct spi_slave));
+	if (!slave)
+		return NULL;
+
+	slave->bus = bus;
+	slave->cs = cs;
+
+	/*
+	 * TODO: Some of the code in spi_init() should probably move
+	 * here, or into spi_claim_bus() below.
+	 */
+
+	return slave;
+}
+
+void spi_free_slave(struct spi_slave *slave)
+{
+	free(slave);
+}
+
 void spi_init(void)
 {
 	volatile spi8xxx_t *spi = &((immap_t *) (CFG_IMMR))->spi;
@@ -53,7 +82,18 @@ void spi_init(void)
 	spi->com = 0;		/* LST bit doesn't do anything, so disregard */
 }
 
-int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
+int spi_claim_bus(struct spi_slave *slave)
+{
+	return 0;
+}
+
+void spi_release_bus(struct spi_slave *slave)
+{
+
+}
+
+int spi_xfer(struct spi_slave *slave, unsigned int bitlen, const void *dout,
+		void *din, unsigned long flags)
 {
 	volatile spi8xxx_t *spi = &((immap_t *) (CFG_IMMR))->spi;
 	unsigned int tmpdout, tmpdin, event;
@@ -61,11 +101,11 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 	int tm, isRead = 0;
 	unsigned char charSize = 32;
 
-	debug("spi_xfer: chipsel %08X dout %08X din %08X bitlen %d\n",
-	      (int)chipsel, *(uint *) dout, *(uint *) din, bitlen);
+	debug("spi_xfer: slave %u:%u dout %08X din %08X bitlen %u\n",
+	      slave->bus, slave->cs, *(uint *) dout, *(uint *) din, bitlen);
 
-	if (chipsel != NULL)
-		(*chipsel) (1);	/* select the target chip */
+	if (flags & SPI_XFER_BEGIN)
+		spi_cs_activate(slave);
 
 	spi->event = 0xffffffff;	/* Clear all SPI events */
 
@@ -135,8 +175,8 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 		debug("*** spi_xfer: transfer ended. Value=%08x\n", tmpdin);
 	}
 
-	if (chipsel != NULL)
-		(*chipsel) (0);	/* deselect the target chip */
+	if (flags & SPI_XFER_END)
+		spi_cs_deactivate(slave);
 
 	return 0;
 }

drivers/spi/mxc_spi.c

@@ -19,6 +19,7 @@
  */
 
 #include <common.h>
+#include <malloc.h>
 #include <spi.h>
 #include <asm/io.h>
 
@@ -61,17 +62,18 @@ static unsigned long spi_bases[] = {
 	0x53f84000,
 };
 
-static unsigned long spi_base;
-
 #endif
 
-spi_chipsel_type spi_chipsel[] = {
-	(spi_chipsel_type)0,
-	(spi_chipsel_type)1,
-	(spi_chipsel_type)2,
-	(spi_chipsel_type)3,
+struct mxc_spi_slave {
+	struct spi_slave slave;
+	unsigned long	base;
+	u32		ctrl_reg;
 };
-int spi_chipsel_cnt = sizeof(spi_chipsel) / sizeof(spi_chipsel[0]);
+
+static inline struct mxc_spi_slave *to_mxc_spi_slave(struct spi_slave *slave)
+{
+	return container_of(slave, struct mxc_spi_slave, slave);
+}
 
 static inline u32 reg_read(unsigned long addr)
 {
@@ -83,30 +85,31 @@ static inline void reg_write(unsigned long addr, u32 val)
 	*(volatile unsigned long*)addr = val;
 }
 
-static u32 spi_xchg_single(u32 data, int bitlen)
+static u32 spi_xchg_single(struct spi_slave *slave, u32 data, int bitlen)
 {
-
-	unsigned int cfg_reg = reg_read(spi_base + MXC_CSPICTRL);
+	struct mxc_spi_slave *mxcs = to_mxc_spi_slave(slave);
+	unsigned int cfg_reg = reg_read(mxcs->base + MXC_CSPICTRL);
 
 	if (MXC_CSPICTRL_BITCOUNT(bitlen - 1) != (cfg_reg & MXC_CSPICTRL_BITCOUNT(31))) {
 		cfg_reg = (cfg_reg & ~MXC_CSPICTRL_BITCOUNT(31)) |
 			MXC_CSPICTRL_BITCOUNT(bitlen - 1);
-		reg_write(spi_base + MXC_CSPICTRL, cfg_reg);
+		reg_write(mxcs->base + MXC_CSPICTRL, cfg_reg);
 	}
 
-	reg_write(spi_base + MXC_CSPITXDATA, data);
+	reg_write(mxcs->base + MXC_CSPITXDATA, data);
 
 	cfg_reg |= MXC_CSPICTRL_XCH;
 
-	reg_write(spi_base + MXC_CSPICTRL, cfg_reg);
+	reg_write(mxcs->base + MXC_CSPICTRL, cfg_reg);
 
-	while (reg_read(spi_base + MXC_CSPICTRL) & MXC_CSPICTRL_XCH)
+	while (reg_read(mxcs->base + MXC_CSPICTRL) & MXC_CSPICTRL_XCH)
 		;
 
-	return reg_read(spi_base + MXC_CSPIRXDATA);
+	return reg_read(mxcs->base + MXC_CSPIRXDATA);
 }
 
-int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
+int spi_xfer(struct spi_slave *slave, unsigned int bitlen, const void *dout,
+		void *din, unsigned long flags)
 {
 	int n_blks = (bitlen + 31) / 32;
 	u32 *out_l, *in_l;
@@ -117,13 +120,10 @@ int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din)
 		return 1;
 	}
 
-	if (!spi_base)
-		spi_select(CONFIG_MXC_SPI_IFACE, (int)chipsel, SPI_MODE_2 | SPI_CS_HIGH);
-
 	for (i = 0, in_l = (u32 *)din, out_l = (u32 *)dout;
 	     i < n_blks;
 	     i++, in_l++, out_l++, bitlen -= 32)
-		*in_l = spi_xchg_single(*out_l, bitlen);
+		*in_l = spi_xchg_single(slave, *out_l, bitlen);
 
 	return 0;
 }
@@ -132,17 +132,17 @@ void spi_init(void)
 {
 }
 
-int spi_select(unsigned int bus, unsigned int dev, unsigned long mode)
+struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
+			unsigned int max_hz, unsigned int mode)
 {
 	unsigned int ctrl_reg;
+	struct mxc_spi_slave *mxcs;
 
 	if (bus >= sizeof(spi_bases) / sizeof(spi_bases[0]) ||
-	    dev > 3)
-		return 1;
-
-	spi_base = spi_bases[bus];
+	    cs > 3)
+		return NULL;
 
-	ctrl_reg = MXC_CSPICTRL_CHIPSELECT(dev) |
+	ctrl_reg = MXC_CSPICTRL_CHIPSELECT(cs) |
 		MXC_CSPICTRL_BITCOUNT(31) |
 		MXC_CSPICTRL_DATARATE(7) | /* FIXME: calculate data rate */
 		MXC_CSPICTRL_EN |
@@ -155,12 +155,38 @@ int spi_select(unsigned int bus, unsigned int dev, unsigned long mode)
 	if (mode & SPI_CS_HIGH)
 		ctrl_reg |= MXC_CSPICTRL_SSPOL;
 
-	reg_write(spi_base + MXC_CSPIRESET, 1);
+	mxcs = malloc(sizeof(struct mxc_spi_slave));
+	if (!mxcs)
+		return NULL;
+
+	mxcs->slave.bus = bus;
+	mxcs->slave.cs = cs;
+	mxcs->base = spi_bases[bus];
+	mxcs->ctrl_reg = ctrl_reg;
+
+	return &mxcs->slave;
+}
+
+void spi_free_slave(struct spi_slave *slave)
+{
+	free(slave);
+}
+
+int spi_claim_bus(struct spi_slave *slave)
+{
+	struct mxc_spi_slave *mxcs = to_mxc_spi_slave(slave);
+
+	reg_write(mxcs->base + MXC_CSPIRESET, 1);
 	udelay(1);
-	reg_write(spi_base + MXC_CSPICTRL, ctrl_reg);
-	reg_write(spi_base + MXC_CSPIPERIOD,
+	reg_write(mxcs->base + MXC_CSPICTRL, mxcs->ctrl_reg);
+	reg_write(mxcs->base + MXC_CSPIPERIOD,
 		  MXC_CSPIPERIOD_32KHZ);
-	reg_write(spi_base + MXC_CSPIINT, 0);
+	reg_write(mxcs->base + MXC_CSPIINT, 0);
 
 	return 0;
 }
+
+void spi_release_bus(struct spi_slave *slave)
+{
+	/* TODO: Shut the controller down */
+}

include/configs/imx31_litekit.h

@@ -65,7 +65,8 @@
 
 #define CONFIG_HARD_SPI		1
 #define CONFIG_MXC_SPI		1
-#define CONFIG_MXC_SPI_IFACE	1
+#define CONFIG_DEFAULT_SPI_BUS	1
+#define CONFIG_DEFAULT_SPI_MODE	(SPI_MODE_2 | SPI_CS_HIGH)
 
 #define CONFIG_RTC_MC13783	1
 

include/configs/mx31ads.h

@@ -62,7 +62,8 @@
 
 #define CONFIG_HARD_SPI		1
 #define CONFIG_MXC_SPI		1
-#define CONFIG_MXC_SPI_IFACE	1	/* Default SPI interface number */
+#define CONFIG_DEFAULT_SPI_BUS	1
+#define CONFIG_DEFAULT_SPI_MODE	(SPI_MODE_2 | SPI_CS_HIGH)
 
 #define CONFIG_RTC_MC13783	1
 

include/spi.h

@@ -31,22 +31,87 @@
 #define	SPI_MODE_1	(0|SPI_CPHA)
 #define	SPI_MODE_2	(SPI_CPOL|0)
 #define	SPI_MODE_3	(SPI_CPOL|SPI_CPHA)
-#define	SPI_CS_HIGH	0x04			/* chipselect active high? */
+#define	SPI_CS_HIGH	0x04			/* CS active high */
 #define	SPI_LSB_FIRST	0x08			/* per-word bits-on-wire */
 #define	SPI_3WIRE	0x10			/* SI/SO signals shared */
 #define	SPI_LOOP	0x20			/* loopback mode */
 
-/*
- * The function call pointer type used to drive the chip select.
- */
-typedef void (*spi_chipsel_type)(int cs);
+/* SPI transfer flags */
+#define SPI_XFER_BEGIN	0x01			/* Assert CS before transfer */
+#define SPI_XFER_END	0x02			/* Deassert CS after transfer */
 
+/*-----------------------------------------------------------------------
+ * Representation of a SPI slave, i.e. what we're communicating with.
+ *
+ * Drivers are expected to extend this with controller-specific data.
+ *
+ *   bus:	ID of the bus that the slave is attached to.
+ *   cs:	ID of the chip select connected to the slave.
+ */
+struct spi_slave {
+	unsigned int	bus;
+	unsigned int	cs;
+};
 
 /*-----------------------------------------------------------------------
  * Initialization, must be called once on start up.
+ *
+ * TODO: I don't think we really need this.
  */
 void spi_init(void);
 
+/*-----------------------------------------------------------------------
+ * Set up communications parameters for a SPI slave.
+ *
+ * This must be called once for each slave. Note that this function
+ * usually doesn't touch any actual hardware, it only initializes the
+ * contents of spi_slave so that the hardware can be easily
+ * initialized later.
+ *
+ *   bus:     Bus ID of the slave chip.
+ *   cs:      Chip select ID of the slave chip on the specified bus.
+ *   max_hz:  Maximum SCK rate in Hz.
+ *   mode:    Clock polarity, clock phase and other parameters.
+ *
+ * Returns: A spi_slave reference that can be used in subsequent SPI
+ * calls, or NULL if one or more of the parameters are not supported.
+ */
+struct spi_slave *spi_setup_slave(unsigned int bus, unsigned int cs,
+		unsigned int max_hz, unsigned int mode);
+
+/*-----------------------------------------------------------------------
+ * Free any memory associated with a SPI slave.
+ *
+ *   slave:	The SPI slave
+ */
+void spi_free_slave(struct spi_slave *slave);
+
+/*-----------------------------------------------------------------------
+ * Claim the bus and prepare it for communication with a given slave.
+ *
+ * This must be called before doing any transfers with a SPI slave. It
+ * will enable and initialize any SPI hardware as necessary, and make
+ * sure that the SCK line is in the correct idle state. It is not
+ * allowed to claim the same bus for several slaves without releasing
+ * the bus in between.
+ *
+ *   slave:	The SPI slave
+ *
+ * Returns: 0 if the bus was claimed successfully, or a negative value
+ * if it wasn't.
+ */
+int spi_claim_bus(struct spi_slave *slave);
+
+/*-----------------------------------------------------------------------
+ * Release the SPI bus
+ *
+ * This must be called once for every call to spi_claim_bus() after
+ * all transfers have finished. It may disable any SPI hardware as
+ * appropriate.
+ *
+ *   slave:	The SPI slave
+ */
+void spi_release_bus(struct spi_slave *slave);
 
 /*-----------------------------------------------------------------------
  * SPI transfer
@@ -60,28 +125,67 @@ void spi_init(void);
  * input data overwrites the output data (since both are buffered by
  * temporary variables, this is OK).
  *
- * If the chipsel() function is not NULL, it is called with a parameter
- * of '1' (chip select active) at the start of the transfer and again with
- * a parameter of '0' at the end of the transfer.
- *
- * If the chipsel() function _is_ NULL, it the responsibility of the
- * caller to make the appropriate chip select active before calling
- * spi_xfer() and making it inactive after spi_xfer() returns.
- *
  * spi_xfer() interface:
- *   chipsel: Routine to call to set/clear the chip select:
- *              if chipsel is NULL, it is not used.
- *              if(cs),  make the chip select active (typically '0').
- *              if(!cs), make the chip select inactive (typically '1').
- *   dout:    Pointer to a string of bits to send out.  The bits are
- *              held in a byte array and are sent MSB first.
- *   din:     Pointer to a string of bits that will be filled in.
- *   bitlen:  How many bits to write and read.
+ *   slave:	The SPI slave which will be sending/receiving the data.
+ *   bitlen:	How many bits to write and read.
+ *   dout:	Pointer to a string of bits to send out.  The bits are
+ *		held in a byte array and are sent MSB first.
+ *   din:	Pointer to a string of bits that will be filled in.
+ *   flags:	A bitwise combination of SPI_XFER_* flags.
  *
  *   Returns: 0 on success, not 0 on failure
  */
-int spi_xfer(spi_chipsel_type chipsel, int bitlen, uchar *dout, uchar *din);
+int  spi_xfer(struct spi_slave *slave, unsigned int bitlen, const void *dout,
+		void *din, unsigned long flags);
+
+/*-----------------------------------------------------------------------
+ * Determine if a SPI chipselect is valid.
+ * This function is provided by the board if the low-level SPI driver
+ * needs it to determine if a given chipselect is actually valid.
+ *
+ * Returns: 1 if bus:cs identifies a valid chip on this board, 0
+ * otherwise.
+ */
+int  spi_cs_is_valid(unsigned int bus, unsigned int cs);
+
+/*-----------------------------------------------------------------------
+ * Activate a SPI chipselect.
+ * This function is provided by the board code when using a driver
+ * that can't control its chipselects automatically (e.g.
+ * common/soft_spi.c). When called, it should activate the chip select
+ * to the device identified by "slave".
+ */
+void spi_cs_activate(struct spi_slave *slave);
+
+/*-----------------------------------------------------------------------
+ * Deactivate a SPI chipselect.
+ * This function is provided by the board code when using a driver
+ * that can't control its chipselects automatically (e.g.
+ * common/soft_spi.c). When called, it should deactivate the chip
+ * select to the device identified by "slave".
+ */
+void spi_cs_deactivate(struct spi_slave *slave);
+
+/*-----------------------------------------------------------------------
+ * Write 8 bits, then read 8 bits.
+ *   slave:	The SPI slave we're communicating with
+ *   byte:	Byte to be written
+ *
+ * Returns: The value that was read, or a negative value on error.
+ *
+ * TODO: This function probably shouldn't be inlined.
+ */
+static inline int spi_w8r8(struct spi_slave *slave, unsigned char byte)
+{
+	unsigned char dout[2];
+	unsigned char din[2];
+	int ret;
+
+	dout[0] = byte;
+	dout[1] = 0;
 
-int spi_select(unsigned int bus, unsigned int dev, unsigned long mode);
+	ret = spi_xfer(slave, 16, dout, din, SPI_XFER_BEGIN | SPI_XFER_END);
+	return ret < 0 ? ret : din[1];
+}
 
 #endif	/* _SPI_H_ */