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Diffstat (limited to 'kernel/include/linux/spi/spi_gpio.h')
| -rw-r--r-- | kernel/include/linux/spi/spi_gpio.h | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/kernel/include/linux/spi/spi_gpio.h b/kernel/include/linux/spi/spi_gpio.h new file mode 100644 index 000000000..1634ce31c --- /dev/null +++ b/kernel/include/linux/spi/spi_gpio.h @@ -0,0 +1,71 @@ +#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 chipselect is not used (there's only one device on the bus), assign + * SPI_GPIO_NO_CHIPSELECT to the controller_data: + * .controller_data = (void *) SPI_GPIO_NO_CHIPSELECT; + * + * If the MISO or MOSI pin is not available then it should be set to + * SPI_GPIO_NO_MISO or SPI_GPIO_NO_MOSI. + * + * If the bitbanged bus is later switched to a "native" controller, + * that platform_device and controller_data should be removed. + */ + +#define SPI_GPIO_NO_CHIPSELECT ((unsigned long)-1l) +#define SPI_GPIO_NO_MISO ((unsigned long)-1l) +#define SPI_GPIO_NO_MOSI ((unsigned long)-1l) + +/** + * 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 long mosi; + unsigned long miso; + + u16 num_chipselect; +}; + +#endif /* __LINUX_SPI_GPIO_H */ |