1 files changed, 71 insertions, 0 deletions
diff --git a/include/linux/spi/spi_gpio.h b/include/linux/spi/spi_gpio.h
new file mode 100644
index 000000000..1634ce31c
--- /dev/null
+++ b/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 */