diff options
| author | David Brownell <david-b@pacbell.net> | 2008-03-04 14:28:27 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-03-04 16:35:10 -0800 |
| commit | 7560fa60fcdcdb0da662f6a9fad9064b554ef46c (patch) | |
| tree | 2089d826b0b9230752f318b20884dca20b3847d5 /Documentation/gpio.txt | |
| parent | 83c7c693ed3e61535ad6a097ad991a88aafc54b8 (diff) | |
gpio: <linux/gpio.h> and "no GPIO support here" stubs
Add a <linux/gpio.h> defining fail/warn stubs for GPIO calls on platforms that
don't support the GPIO programming interface. That includes the arch-specific
implementation glue otherwise.
This facilitates a new model for GPIO usage: drivers that can use GPIOs if
they're available, but don't require them. One example of such a driver is
NAND driver for various FreeScale chips. On platforms update with GPIO
support, they can be used instead of a worst-case delay to verify that the
BUSY signal is off.
(Also includes a couple minor unrelated doc updates.)
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/gpio.txt')
| -rw-r--r-- | Documentation/gpio.txt | 16 |
1 files changed, 12 insertions, 4 deletions
diff --git a/Documentation/gpio.txt b/Documentation/gpio.txt index 8da724e2a0ff..54630095aa3c 100644 --- a/Documentation/gpio.txt +++ b/Documentation/gpio.txt @@ -2,6 +2,9 @@ GPIO Interfaces This provides an overview of GPIO access conventions on Linux. +These calls use the gpio_* naming prefix. No other calls should use that +prefix, or the related __gpio_* prefix. + What is a GPIO? =============== @@ -69,11 +72,13 @@ in this document, but drivers acting as clients to the GPIO interface must not care how it's implemented.) That said, if the convention is supported on their platform, drivers should -use it when possible. Platforms should declare GENERIC_GPIO support in -Kconfig (boolean true), which multi-platform drivers can depend on when -using the include file: +use it when possible. Platforms must declare GENERIC_GPIO support in their +Kconfig (boolean true), and provide an <asm/gpio.h> file. Drivers that can't +work without standard GPIO calls should have Kconfig entries which depend +on GENERIC_GPIO. The GPIO calls are available, either as "real code" or as +optimized-away stubs, when drivers use the include file: - #include <asm/gpio.h> + #include <linux/gpio.h> If you stick to this convention then it'll be easier for other developers to see what your code is doing, and help maintain it. @@ -316,6 +321,9 @@ pulldowns integrated on some platforms. Not all platforms support them, or support them in the same way; and any given board might use external pullups (or pulldowns) so that the on-chip ones should not be used. (When a circuit needs 5 kOhm, on-chip 100 kOhm resistors won't do.) +Likewise drive strength (2 mA vs 20 mA) and voltage (1.8V vs 3.3V) is a +platform-specific issue, as are models like (not) having a one-to-one +correspondence between configurable pins and GPIOs. There are other system-specific mechanisms that are not specified here, like the aforementioned options for input de-glitching and wire-OR output. |