--- /dev/null
+PXA2xx SPI on SSP driver HOWTO
+===================================================
+This a mini howto on the pxa2xx_spi driver. The driver turns a PXA2xx
+synchronous serial port into a SPI master controller
+(see Documentation/spi/spi_summary). The driver has the following features
+
+- Support for any PXA2xx SSP
+- SSP PIO and SSP DMA data transfers.
+- External and Internal (SSPFRM) chip selects.
+- Per slave device (chip) configuration.
+- Full suspend, freeze, resume support.
+
+The driver is built around a "spi_message" fifo serviced by workqueue and a
+tasklet. The workqueue, "pump_messages", drives message fifo and the tasklet
+(pump_transfer) is responsible for queuing SPI transactions and setting up and
+launching the dma/interrupt driven transfers.
+
+Declaring PXA2xx Master Controllers
+-----------------------------------
+Typically a SPI master is defined in the arch/.../mach-*/board-*.c as a
+"platform device". The master configuration is passed to the driver via a table
+found in include/asm-arm/arch-pxa/pxa2xx_spi.h:
+
+struct pxa2xx_spi_master {
+ enum pxa_ssp_type ssp_type;
+ u32 clock_enable;
+ u16 num_chipselect;
+ u8 enable_dma;
+};
+
+The "pxa2xx_spi_master.ssp_type" field must have a value between 1 and 3 and
+informs the driver which features a particular SSP supports.
+
+The "pxa2xx_spi_master.clock_enable" field is used to enable/disable the
+corresponding SSP peripheral block in the "Clock Enable Register (CKEN"). See
+the "PXA2xx Developer Manual" section "Clocks and Power Management".
+
+The "pxa2xx_spi_master.num_chipselect" field is used to determine the number of
+slave device (chips) attached to this SPI master.
+
+The "pxa2xx_spi_master.enable_dma" field informs the driver that SSP DMA should
+be used. This caused the driver to acquire two DMA channels: rx_channel and
+tx_channel. The rx_channel has a higher DMA service priority the tx_channel.
+See the "PXA2xx Developer Manual" section "DMA Controller".
+
+NSSP MASTER SAMPLE
+------------------
+Below is a sample configuration using the PXA255 NSSP.
+
+static struct resource pxa_spi_nssp_resources[] = {
+ [0] = {
+ .start = __PREG(SSCR0_P(2)), /* Start address of NSSP */
+ .end = __PREG(SSCR0_P(2)) + 0x2c, /* Range of registers */
+ .flags = IORESOURCE_MEM,
+ },
+ [1] = {
+ .start = IRQ_NSSP, /* NSSP IRQ */
+ .end = IRQ_NSSP,
+ .flags = IORESOURCE_IRQ,
+ },
+};
+
+static struct pxa2xx_spi_master pxa_nssp_master_info = {
+ .ssp_type = PXA25x_NSSP, /* Type of SSP */
+ .clock_enable = CKEN9_NSSP, /* NSSP Peripheral clock */
+ .num_chipselect = 1, /* Matches the number of chips attached to NSSP */
+ .enable_dma = 1, /* Enables NSSP DMA */
+};
+
+static struct platform_device pxa_spi_nssp = {
+ .name = "pxa2xx-spi", /* MUST BE THIS VALUE, so device match driver */
+ .id = 2, /* Bus number, MUST MATCH SSP number 1..n */
+ .resource = pxa_spi_nssp_resources,
+ .num_resources = ARRAY_SIZE(pxa_spi_nssp_resources),
+ .dev = {
+ .platform_data = &pxa_nssp_master_info, /* Passed to driver */
+ },
+};
+
+static struct platform_device *devices[] __initdata = {
+ &pxa_spi_nssp,
+};
+
+static void __init board_init(void)
+{
+ (void)platform_add_device(devices, ARRAY_SIZE(devices));
+}
+
+Declaring Slave Devices
+-----------------------
+Typically each SPI slave (chip) is defined in the arch/.../mach-*/board-*.c
+using the "spi_board_info" structure found in "linux/spi/spi.h". See
+"Documentation/spi/spi_summary" for additional information.
+
+Each slave device attached to the PXA must provide slave specific configuration
+information via the structure "pxa2xx_spi_chip" found in
+"include/asm-arm/arch-pxa/pxa2xx_spi.h". The pxa2xx_spi master controller driver
+will uses the configuration whenever the driver communicates with the slave
+device.
+
+struct pxa2xx_spi_chip {
+ u8 tx_threshold;
+ u8 rx_threshold;
+ u8 dma_burst_size;
+ u32 timeout_microsecs;
+ u8 enable_loopback;
+ void (*cs_control)(u32 command);
+};
+
+The "pxa2xx_spi_chip.tx_threshold" and "pxa2xx_spi_chip.rx_threshold" fields are
+used to configure the SSP hardware fifo. These fields are critical to the
+performance of pxa2xx_spi driver and misconfiguration will result in rx
+fifo overruns (especially in PIO mode transfers). Good default values are
+
+ .tx_threshold = 12,
+ .rx_threshold = 4,
+
+The "pxa2xx_spi_chip.dma_burst_size" field is used to configure PXA2xx DMA
+engine and is related the "spi_device.bits_per_word" field. Read and understand
+the PXA2xx "Developer Manual" sections on the DMA controller and SSP Controllers
+to determine the correct value. An SSP configured for byte-wide transfers would
+use a value of 8.
+
+The "pxa2xx_spi_chip.timeout_microsecs" fields is used to efficiently handle
+trailing bytes in the SSP receiver fifo. The correct value for this field is
+dependent on the SPI bus speed ("spi_board_info.max_speed_hz") and the specific
+slave device. Please note the the PXA2xx SSP 1 does not support trailing byte
+timeouts and must busy-wait any trailing bytes.
+
+The "pxa2xx_spi_chip.enable_loopback" field is used to place the SSP porting
+into internal loopback mode. In this mode the SSP controller internally
+connects the SSPTX pin the the SSPRX pin. This is useful for initial setup
+testing.
+
+The "pxa2xx_spi_chip.cs_control" field is used to point to a board specific
+function for asserting/deasserting a slave device chip select. If the field is
+NULL, the pxa2xx_spi master controller driver assumes that the SSP port is
+configured to use SSPFRM instead.
+
+NSSP SALVE SAMPLE
+-----------------
+The pxa2xx_spi_chip structure is passed to the pxa2xx_spi driver in the
+"spi_board_info.controller_data" field. Below is a sample configuration using
+the PXA255 NSSP.
+
+/* Chip Select control for the CS8415A SPI slave device */
+static void cs8415a_cs_control(u32 command)
+{
+ if (command & PXA2XX_CS_ASSERT)
+ GPCR(2) = GPIO_bit(2);
+ else
+ GPSR(2) = GPIO_bit(2);
+}
+
+/* Chip Select control for the CS8405A SPI slave device */
+static void cs8405a_cs_control(u32 command)
+{
+ if (command & PXA2XX_CS_ASSERT)
+ GPCR(3) = GPIO_bit(3);
+ else
+ GPSR(3) = GPIO_bit(3);
+}
+
+static struct pxa2xx_spi_chip cs8415a_chip_info = {
+ .tx_threshold = 12, /* SSP hardward FIFO threshold */
+ .rx_threshold = 4, /* SSP hardward FIFO threshold */
+ .dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */
+ .timeout_microsecs = 64, /* Wait at least 64usec to handle trailing */
+ .cs_control = cs8415a_cs_control, /* Use external chip select */
+};
+
+static struct pxa2xx_spi_chip cs8405a_chip_info = {
+ .tx_threshold = 12, /* SSP hardward FIFO threshold */
+ .rx_threshold = 4, /* SSP hardward FIFO threshold */
+ .dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */
+ .timeout_microsecs = 64, /* Wait at least 64usec to handle trailing */
+ .cs_control = cs8405a_cs_control, /* Use external chip select */
+};
+
+static struct spi_board_info streetracer_spi_board_info[] __initdata = {
+ {
+ .modalias = "cs8415a", /* Name of spi_driver for this device */
+ .max_speed_hz = 3686400, /* Run SSP as fast a possbile */
+ .bus_num = 2, /* Framework bus number */
+ .chip_select = 0, /* Framework chip select */
+ .platform_data = NULL; /* No spi_driver specific config */
+ .controller_data = &cs8415a_chip_info, /* Master chip config */
+ .irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */
+ },
+ {
+ .modalias = "cs8405a", /* Name of spi_driver for this device */
+ .max_speed_hz = 3686400, /* Run SSP as fast a possbile */
+ .bus_num = 2, /* Framework bus number */
+ .chip_select = 1, /* Framework chip select */
+ .controller_data = &cs8405a_chip_info, /* Master chip config */
+ .irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */
+ },
+};
+
+static void __init streetracer_init(void)
+{
+ spi_register_board_info(streetracer_spi_board_info,
+ ARRAY_SIZE(streetracer_spi_board_info));
+}
+
+
+DMA and PIO I/O Support
+-----------------------
+The pxa2xx_spi driver support both DMA and interrupt driven PIO message
+transfers. The driver defaults to PIO mode and DMA transfers must enabled by
+setting the "enable_dma" flag in the "pxa2xx_spi_master" structure and and
+ensuring that the "pxa2xx_spi_chip.dma_burst_size" field is non-zero. The DMA
+mode support both coherent and stream based DMA mappings.
+
+The following logic is used to determine the type of I/O to be used on
+a per "spi_transfer" basis:
+
+if !enable_dma or dma_burst_size == 0 then
+ always use PIO transfers
+
+if spi_message.is_dma_mapped and rx_dma_buf != 0 and tx_dma_buf != 0 then
+ use coherent DMA mode
+
+if rx_buf and tx_buf are aligned on 8 byte boundary then
+ use streaming DMA mode
+
+otherwise
+ use PIO transfer
+
+THANKS TO
+---------
+
+David Brownell and others for mentoring the development of this driver.
+
git://git.onelab.eu / linux-2.6.git / blobdiff