gpiolib: pcf857x i2c gpio expander support

This is a new-style I2C driver for most common 8 and 16 bit I2C based
"quasi-bidirectional" GPIO expanders: pcf8574 or pcf8575, and several
compatible models (mostly faster, supporting I2C at up to 1 MHz).

The driver exposes the GPIO signals using the platform-neutral GPIO
programming interface, so they are easily accessed by other kernel code.  The
lack of such a flexible kernel API has been a big factor in the proliferation
of board-specific drivers for these chips...  stuff that rarely makes it
upstream since it's so ugly.  This driver will let such boards use standard
calls.

Since it's a new-style driver, these devices must be configured as part of
board-specific init.  That eliminates the need for error-prone manual
configuration of module parameters, and makes compatibility with legacy
drivers (pcf8574.c, pc8575.c) for these chips easier (there's a clear
either/or disjunction).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Jean Delvare <khali@linux-fr.org>
Cc: Eric Miao <eric.miao@marvell.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Haavard Skinnemoen <hskinnemoen@atmel.com>
Cc: Philipp Zabel <philipp.zabel@gmail.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Ben Gardner <bgardner@wabtec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 45 insertions, 0 deletions

diff --git a/include/linux/i2c/pcf857x.h b/include/linux/i2c/pcf857x.h
new file mode 100644
index 000000000000..ba8ea6e16476
--- /dev/null
+++ b/include/linux/i2c/pcf857x.h
@@ -0,0 +1,45 @@
+#ifndef __LINUX_PCF857X_H
+#define __LINUX_PCF857X_H
+
+/**
+ * struct pcf857x_platform_data - data to set up pcf857x driver
+ * @gpio_base: number of the chip's first GPIO
+ * @n_latch: optional bit-inverse of initial register value; if
+ *      you leave this initialized to zero the driver will act
+ *      like the chip was just reset
+ * @setup: optional callback issued once the GPIOs are valid
+ * @teardown: optional callback issued before the GPIOs are invalidated
+ * @context: optional parameter passed to setup() and teardown()
+ *
+ * In addition to the I2C_BOARD_INFO() state appropriate to each chip,
+ * the i2c_board_info used with the pcf875x driver must provide the
+ * chip "type" ("pcf8574", "pcf8574a", "pcf8575", "pcf8575c") and its
+ * platform_data (pointer to one of these structures) with at least
+ * the gpio_base value initialized.
+ *
+ * The @setup callback may be used with the kind of board-specific glue
+ * which hands the (now-valid) GPIOs to other drivers, or which puts
+ * devices in their initial states using these GPIOs.
+ *
+ * These GPIO chips are only "quasi-bidirectional"; read the chip specs
+ * to understand the behavior.  They don't have separate registers to
+ * record which pins are used for input or output, record which output
+ * values are driven, or provide access to input values.  That must be
+ * inferred by reading the chip's value and knowing the last value written
+ * to it.  If you leave n_latch initialized to zero, that last written
+ * value is presumed to be all ones (as if the chip were just reset).
+ */
+struct pcf857x_platform_data {
+        unsigned        gpio_base;
+        unsigned        n_latch;
+
+        int             (*setup)(struct i2c_client *client,
+                                        int gpio, unsigned ngpio,
+                                        void *context);
+        int             (*teardown)(struct i2c_client *client,
+                                        int gpio, unsigned ngpio,
+                                        void *context);
+        void            *context;
+};
+
+#endif /* __LINUX_PCF857X_H */