include/linux/spi/spi_gpio.h

   1 #ifndef __LINUX_SPI_GPIO_H
   2 #define __LINUX_SPI_GPIO_H
   3
   4 /*
   5  * For each bitbanged SPI bus, set up a platform_device node with:
   6  *   - name "spi_gpio"
   7  *   - id the same as the SPI bus number it implements
   8  *   - dev.platform data pointing to a struct spi_gpio_platform_data
   9  *
  10  * Or, see the driver code for information about speedups that are
  11  * possible on platforms that support inlined access for GPIOs (no
  12  * spi_gpio_platform_data is used).
  13  *
  14  * Use spi_board_info with these busses in the usual way, being sure
  15  * that the controller_data being the GPIO used for each device's
  16  * chipselect:
  17  *
  18  *      static struct spi_board_info ... [] = {
  19  *      ...
  20  *              // this slave uses GPIO 42 for its chipselect
  21  *              .controller_data = (void *) 42,
  22  *      ...
  23  *              // this one uses GPIO 86 for its chipselect
  24  *              .controller_data = (void *) 86,
  25  *      ...
  26  *      };
  27  *
  28  * If chipselect is not used (there's only one device on the bus), assign
  29  * SPI_GPIO_NO_CHIPSELECT to the controller_data:
  30  *              .controller_data = (void *) SPI_GPIO_NO_CHIPSELECT;
  31  *
  32  * If the bitbanged bus is later switched to a "native" controller,
  33  * that platform_device and controller_data should be removed.
  34  */
  35
  36 #define SPI_GPIO_NO_CHIPSELECT          ((unsigned long)-1l)
  37
  38 /**
  39  * struct spi_gpio_platform_data - parameter for bitbanged SPI master
  40  * @sck: number of the GPIO used for clock output
  41  * @mosi: number of the GPIO used for Master Output, Slave In (MOSI) data
  42  * @miso: number of the GPIO used for Master Input, Slave Output (MISO) data
  43  * @num_chipselect: how many slaves to allow
  44  *
  45  * All GPIO signals used with the SPI bus managed through this driver
  46  * (chipselects, MOSI, MISO, SCK) must be configured as GPIOs, instead
  47  * of some alternate function.
  48  *
  49  * It can be convenient to use this driver with pins that have alternate
  50  * functions associated with a "native" SPI controller if a driver for that
  51  * controller is not available, or is missing important functionality.
  52  *
  53  * On platforms which can do so, configure MISO with a weak pullup unless
  54  * there's an external pullup on that signal.  That saves power by avoiding
  55  * floating signals.  (A weak pulldown would save power too, but many
  56  * drivers expect to see all-ones data as the no slave "response".)
  57  */
  58 struct spi_gpio_platform_data {
  59         unsigned        sck;
  60         unsigned        mosi;
  61         unsigned        miso;
  62
  63         u16             num_chipselect;
  64 };
  65
  66 #endif /* __LINUX_SPI_GPIO_H */