From d29389de0b0ee1715333bafc6ac3f22a75aa4313 Mon Sep 17 00:00:00 2001 From: David Brownell Date: Tue, 6 Jan 2009 14:41:41 -0800 Subject: spi_gpio driver Generalize the old at91rm9200 "bootstrap" bitbanging SPI master driver as "spi_gpio", so it works with arbitrary GPIOs and can be configured through platform_data. Such SPI masters support: - any number of bus instances (bus_num is the platform_device.id) - any number of chipselects (one GPIO per spi_device) - all four SPI_MODE values, and SPI_CS_HIGH - i/o word sizes from 1 to 32 bits; - devices configured as with any other spi_master controller When configured using platform_data, this provides relatively low clock rates. On platforms that support inlined GPIO calls, significantly improved transfer speeds are also possible with a semi-custom driver. (It's still painful when accessing flash memory, but less so.) Sanity checked by using this version to replace both native controllers on a board with six different SPI slaves, relying on three different SPI_MODE_* values and both SPI_CS_HIGH settings for correct operation. [akpm@linux-foundation.org: cleanups] Signed-off-by: David Brownell Acked-by: Magnus Damm Tested-by: Magnus Damm Cc: Torgil Svensson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/spi/spi_gpio.h | 60 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 60 insertions(+) create mode 100644 include/linux/spi/spi_gpio.h (limited to 'include/linux/spi') diff --git a/include/linux/spi/spi_gpio.h b/include/linux/spi/spi_gpio.h new file mode 100644 index 000000000000..0f01a0f1f40c --- /dev/null +++ b/include/linux/spi/spi_gpio.h @@ -0,0 +1,60 @@ +#ifndef __LINUX_SPI_GPIO_H +#define __LINUX_SPI_GPIO_H + +/* + * For each bitbanged SPI bus, set up a platform_device node with: + * - name "spi_gpio" + * - id the same as the SPI bus number it implements + * - dev.platform data pointing to a struct spi_gpio_platform_data + * + * Or, see the driver code for information about speedups that are + * possible on platforms that support inlined access for GPIOs (no + * spi_gpio_platform_data is used). + * + * Use spi_board_info with these busses in the usual way, being sure + * that the controller_data being the GPIO used for each device's + * chipselect: + * + * static struct spi_board_info ... [] = { + * ... + * // this slave uses GPIO 42 for its chipselect + * .controller_data = (void *) 42, + * ... + * // this one uses GPIO 86 for its chipselect + * .controller_data = (void *) 86, + * ... + * }; + * + * If the bitbanged bus is later switched to a "native" controller, + * that platform_device and controller_data should be removed. + */ + +/** + * struct spi_gpio_platform_data - parameter for bitbanged SPI master + * @sck: number of the GPIO used for clock output + * @mosi: number of the GPIO used for Master Output, Slave In (MOSI) data + * @miso: number of the GPIO used for Master Input, Slave Output (MISO) data + * @num_chipselect: how many slaves to allow + * + * All GPIO signals used with the SPI bus managed through this driver + * (chipselects, MOSI, MISO, SCK) must be configured as GPIOs, instead + * of some alternate function. + * + * It can be convenient to use this driver with pins that have alternate + * functions associated with a "native" SPI controller if a driver for that + * controller is not available, or is missing important functionality. + * + * On platforms which can do so, configure MISO with a weak pullup unless + * there's an external pullup on that signal. That saves power by avoiding + * floating signals. (A weak pulldown would save power too, but many + * drivers expect to see all-ones data as the no slave "response".) + */ +struct spi_gpio_platform_data { + unsigned sck; + unsigned mosi; + unsigned miso; + + u16 num_chipselect; +}; + +#endif /* __LINUX_SPI_GPIO_H */ -- cgit v1.2.1