diff options
Diffstat (limited to 'Documentation/spi')
| -rw-r--r-- | Documentation/spi/pxa2xx.rst | 59 |
1 files changed, 28 insertions, 31 deletions
diff --git a/Documentation/spi/pxa2xx.rst b/Documentation/spi/pxa2xx.rst index 04f2a3856c40..19479b801826 100644 --- a/Documentation/spi/pxa2xx.rst +++ b/Documentation/spi/pxa2xx.rst @@ -3,13 +3,13 @@ PXA2xx SPI on SSP driver HOWTO ============================== This a mini HOWTO on the pxa2xx_spi driver. The driver turns a PXA2xx -synchronous serial port into an SPI master controller +synchronous serial port into an SPI host controller (see Documentation/spi/spi-summary.rst). The driver has the following features - Support for any PXA2xx and compatible SSP. - SSP PIO and SSP DMA data transfers. - External and Internal (SSPFRM) chip selects. -- Per slave device (chip) configuration. +- Per peripheral device (chip) configuration. - Full suspend, freeze, resume support. The driver is built around a &struct spi_message FIFO serviced by kernel @@ -17,10 +17,10 @@ thread. The kernel thread, spi_pump_messages(), drives message FIFO and is responsible for queuing SPI transactions and setting up and launching the DMA or interrupt driven transfers. -Declaring PXA2xx Master Controllers ------------------------------------ -Typically, for a legacy platform, an SPI master is defined in the -arch/.../mach-*/board-*.c as a "platform device". The master configuration +Declaring PXA2xx host controllers +--------------------------------- +Typically, for a legacy platform, an SPI host controller is defined in the +arch/.../mach-*/board-*.c as a "platform device". The host controller configuration is passed to the driver via a table found in include/linux/spi/pxa2xx_spi.h:: struct pxa2xx_spi_controller { @@ -30,7 +30,7 @@ is passed to the driver via a table found in include/linux/spi/pxa2xx_spi.h:: }; The "pxa2xx_spi_controller.num_chipselect" field is used to determine the number of -slave device (chips) attached to this SPI master. +peripheral devices (chips) attached to this SPI host controller. The "pxa2xx_spi_controller.enable_dma" field informs the driver that SSP DMA should be used. This caused the driver to acquire two DMA channels: Rx channel and @@ -40,8 +40,8 @@ See the "PXA2xx Developer Manual" section "DMA Controller". For the new platforms the description of the controller and peripheral devices comes from Device Tree or ACPI. -NSSP MASTER SAMPLE ------------------- +NSSP HOST SAMPLE +---------------- Below is a sample configuration using the PXA255 NSSP for a legacy platform:: static struct resource pxa_spi_nssp_resources[] = { @@ -57,7 +57,7 @@ Below is a sample configuration using the PXA255 NSSP for a legacy platform:: }, }; - static struct pxa2xx_spi_controller pxa_nssp_master_info = { + static struct pxa2xx_spi_controller pxa_nssp_controller_info = { .num_chipselect = 1, /* Matches the number of chips attached to NSSP */ .enable_dma = 1, /* Enables NSSP DMA */ }; @@ -68,7 +68,7 @@ Below is a sample configuration using the PXA255 NSSP for a legacy platform:: .resource = pxa_spi_nssp_resources, .num_resources = ARRAY_SIZE(pxa_spi_nssp_resources), .dev = { - .platform_data = &pxa_nssp_master_info, /* Passed to driver */ + .platform_data = &pxa_nssp_controller_info, /* Passed to driver */ }, }; @@ -81,17 +81,17 @@ Below is a sample configuration using the PXA255 NSSP for a legacy platform:: (void)platform_add_device(devices, ARRAY_SIZE(devices)); } -Declaring Slave Devices ------------------------ -Typically, for a legacy platform, each SPI slave (chip) is defined in the +Declaring peripheral devices +---------------------------- +Typically, for a legacy platform, each SPI peripheral device (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.rst" for additional information. -Each slave device attached to the PXA must provide slave specific configuration +Each peripheral device (chip) attached to the PXA2xx must provide specific chip configuration information via the structure "pxa2xx_spi_chip" found in -"include/linux/spi/pxa2xx_spi.h". The pxa2xx_spi master controller driver -will uses the configuration whenever the driver communicates with the slave +"include/linux/spi/pxa2xx_spi.h". The PXA2xx host controller driver will use +the configuration whenever the driver communicates with the peripheral device. All fields are optional. :: @@ -123,7 +123,7 @@ dma_burst_size == 0. 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 +peripheral device. Please note that the PXA2xx SSP 1 does not support trailing byte timeouts and must busy-wait any trailing bytes. NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the @@ -132,8 +132,8 @@ asserted around the complete message. Use SSPFRM as a GPIO (through a descriptor to accommodate these chips. -NSSP SLAVE SAMPLE ------------------ +NSSP PERIPHERAL SAMPLE +---------------------- For a legacy platform or in some other cases, 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. @@ -161,16 +161,16 @@ field. Below is a sample configuration using the PXA255 NSSP. .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 */ + .controller_data = &cs8415a_chip_info, /* Host controller config */ + .irq = STREETRACER_APCI_IRQ, /* Peripheral device interrupt */ }, { .modalias = "cs8405a", /* Name of spi_driver for this device */ .max_speed_hz = 3686400, /* Run SSP as fast a possible */ .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 */ + .controller_data = &cs8405a_chip_info, /* Host controller config */ + .irq = STREETRACER_APCI_IRQ, /* Peripheral device interrupt */ }, }; @@ -193,17 +193,14 @@ 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 then - always use PIO transfers + if spi_message.len > 65536 then + if spi_message.is_dma_mapped or rx_dma_buf != 0 or tx_dma_buf != 0 then + reject premapped 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 - - if rx_buf and tx_buf are aligned on 8 byte boundary then + if enable_dma and the size is in the range [DMA burst size..65536] then use streaming DMA mode otherwise |