-\feffPXA2xx SPI on SSP driver HOWTO
+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
-----------------------------------
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:
+found in arch/arm/mach-pxa/include/mach/pxa2xx_spi.h:
struct pxa2xx_spi_master {
enum pxa_ssp_type ssp_type;
static struct pxa2xx_spi_master pxa_nssp_master_info = {
.ssp_type = PXA25x_NSSP, /* Type of SSP */
- .clock_enable = CKEN9_NSSP, /* NSSP Peripheral clock */
+ .clock_enable = CKEN_NSSP, /* NSSP Peripheral clock */
.num_chipselect = 1, /* Matches the number of chips attached to NSSP */
.enable_dma = 1, /* Enables NSSP DMA */
};
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
+"arch/arm/mach-pxa/include/mach/pxa2xx_spi.h". The pxa2xx_spi master controller driver
will uses the configuration whenever the driver communicates with the slave
-device.
+device. All fields are optional.
struct pxa2xx_spi_chip {
u8 tx_threshold;
u8 rx_threshold;
u8 dma_burst_size;
- u32 timeout_microsecs;
+ u32 timeout;
u8 enable_loopback;
void (*cs_control)(u32 command);
};
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,
+ .tx_threshold = 8,
+ .rx_threshold = 8,
+
+The range is 1 to 16 where zero indicates "use default".
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.
+use a value of 8. The driver will determine a reasonable default if
+dma_burst_size == 0.
-The "pxa2xx_spi_chip.timeout_microsecs" fields is used to efficiently handle
+The "pxa2xx_spi_chip.timeout" 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 that the PXA2xx SSP 1 does not support trailing byte
NULL, the pxa2xx_spi master controller driver assumes that the SSP port is
configured to use SSPFRM instead.
-NSSP SALVE SAMPLE
+NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the
+chipselect is dropped after each spi_transfer. Most devices need chip select
+asserted around the complete message. Use SSPFRM as a GPIO (through cs_control)
+to accomodate these chips.
+
+
+NSSP SLAVE 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
}
static struct pxa2xx_spi_chip cs8415a_chip_info = {
- .tx_threshold = 12, /* SSP hardward FIFO threshold */
- .rx_threshold = 4, /* SSP hardward FIFO threshold */
+ .tx_threshold = 8, /* SSP hardward FIFO threshold */
+ .rx_threshold = 8, /* 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 */
+ .timeout = 235, /* See Intel documentation */
.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 */
+ .tx_threshold = 8, /* SSP hardward FIFO threshold */
+ .rx_threshold = 8, /* 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 */
+ .timeout = 235, /* See Intel documentation */
.cs_control = cs8405a_cs_control, /* Use external chip select */
};
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
-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 pxa2xx_spi driver supports both DMA and interrupt driven PIO message
+transfers. The driver defaults to PIO mode and DMA transfers must be enabled
+by setting the "enable_dma" flag in the "pxa2xx_spi_master" structure. The DMA
+mode supports 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
+if !enable_dma then
always use PIO transfers
+if spi_message.len > 8191 then
+ print "rate limited" warning
+ use PIO transfers
+
if spi_message.is_dma_mapped and rx_dma_buf != 0 and tx_dma_buf != 0 then
use coherent DMA mode
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