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, 23 insertions, 0 deletions

diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 560687c4667e..36d5d6aefc0e 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -27,6 +27,29 @@ config DEBUG_GPIO
 
 comment "I2C GPIO expanders:"
 
+config GPIO_PCF857X
+        tristate "PCF857x, PCA857x, and PCA967x I2C GPIO expanders"
+        depends on I2C
+        help
+          Say yes here to provide access to most "quasi-bidirectional" I2C
+          GPIO expanders used for additional digital outputs or inputs.
+          Most of these parts are from NXP, though TI is a second source for
+          some of them.  Compatible models include:
+
+          8 bits:   pcf8574, pcf8574a, pca8574, pca8574a,
+                    pca9670, pca9672, pca9674, pca9674a
+
+          16 bits:  pcf8575, pcf8575c, pca8575,
+                    pca9671, pca9673, pca9675
+
+          Your board setup code will need to declare the expanders in
+          use, and assign numbers to the GPIOs they expose.  Those GPIOs
+          can then be used from drivers and other kernel code, just like
+          other GPIOs, but only accessible from task contexts.
+
+          This driver provides an in-kernel interface to those GPIOs using
+          platform-neutral GPIO calls.
+
 comment "SPI GPIO expanders:"
 
 endmenu