include/linux/spi/spi_gpio.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef __LINUX_SPI_GPIO_H
   3 #define __LINUX_SPI_GPIO_H
   4
   5 /*
   6  * For each bitbanged SPI bus, set up a platform_device node with:
   7  *   - name "spi_gpio"
   8  *   - id the same as the SPI bus number it implements
   9  *   - dev.platform data pointing to a struct spi_gpio_platform_data
  10  *
  11  * Or, see the driver code for information about speedups that are
  12  * possible on platforms that support inlined access for GPIOs (no
  13  * spi_gpio_platform_data is used).
  14  *
  15  * Use spi_board_info with these busses in the usual way, being sure
  16  * that the controller_data being the GPIO used for each device's
  17  * chipselect:
  18  *
  19  *      static struct spi_board_info ... [] = {
  20  *      ...
  21  *              // this slave uses GPIO 42 for its chipselect
  22  *              .controller_data = (void *) 42,
  23  *      ...
  24  *              // this one uses GPIO 86 for its chipselect
  25  *              .controller_data = (void *) 86,
  26  *      ...
  27  *      };
  28  *
  29  * If chipselect is not used (there's only one device on the bus), assign
  30  * SPI_GPIO_NO_CHIPSELECT to the controller_data:
  31  *              .controller_data = (void *) SPI_GPIO_NO_CHIPSELECT;
  32  *
  33  * If the MISO or MOSI pin is not available then it should be set to
  34  * SPI_GPIO_NO_MISO or SPI_GPIO_NO_MOSI.
  35  *
  36  * If the bitbanged bus is later switched to a "native" controller,
  37  * that platform_device and controller_data should be removed.
  38  */
  39
  40 #define SPI_GPIO_NO_CHIPSELECT          ((unsigned long)-1l)
  41 #define SPI_GPIO_NO_MISO                ((unsigned long)-1l)
  42 #define SPI_GPIO_NO_MOSI                ((unsigned long)-1l)
  43
  44 /**
  45  * struct spi_gpio_platform_data - parameter for bitbanged SPI master
  46  * @sck: number of the GPIO used for clock output
  47  * @mosi: number of the GPIO used for Master Output, Slave In (MOSI) data
  48  * @miso: number of the GPIO used for Master Input, Slave Output (MISO) data
  49  * @num_chipselect: how many slaves to allow
  50  *
  51  * All GPIO signals used with the SPI bus managed through this driver
  52  * (chipselects, MOSI, MISO, SCK) must be configured as GPIOs, instead
  53  * of some alternate function.
  54  *
  55  * It can be convenient to use this driver with pins that have alternate
  56  * functions associated with a "native" SPI controller if a driver for that
  57  * controller is not available, or is missing important functionality.
  58  *
  59  * On platforms which can do so, configure MISO with a weak pullup unless
  60  * there's an external pullup on that signal.  That saves power by avoiding
  61  * floating signals.  (A weak pulldown would save power too, but many
  62  * drivers expect to see all-ones data as the no slave "response".)
  63  */
  64 struct spi_gpio_platform_data {
  65         unsigned        sck;
  66         unsigned long   mosi;
  67         unsigned long   miso;
  68
  69         u16             num_chipselect;
  70 };
  71
  72 #endif /* __LINUX_SPI_GPIO_H */