[PATCH] gpio: document how to order GPIO controllers
From: robh@kernel.org (Rob Herring)
Date: 2016-07-05 14:05:46
Also in:
linux-devicetree, linux-gpio
On Fri, Jul 01, 2016 at 08:42:13AM +0200, Uwe Kleine-K?nig wrote:
This uses the same approach that is already used for spi, i2c and several other controllers to ensure a consistent numbering independent of probe order. This is in use for several gpio drivers that already now use of_alias_get_id(np, "gpio").
Like SPI and I2C, I'm against further abuse of aliases for this purpose [1].
quoted hunk ↗ jump to hunk
Signed-off-by: Uwe Kleine-K?nig <redacted> --- Hello, Linus requested such a patch as part of a change that introduces this mechanism to the gpio-omap driver[1]. IMHO this is better done in a separate patch, so here it comes. Best regards Uwe [1] http://thread.gmane.org/gmane.linux.kernel.gpio/17399/focus=17629 Documentation/devicetree/bindings/gpio/gpio.txt | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)diff --git a/Documentation/devicetree/bindings/gpio/gpio.txt b/Documentation/devicetree/bindings/gpio/gpio.txt index 68d28f62a6f4..5dbacc8f094a 100644 --- a/Documentation/devicetree/bindings/gpio/gpio.txt +++ b/Documentation/devicetree/bindings/gpio/gpio.txt@@ -227,6 +227,24 @@ Example of two SOC GPIO banks defined as gpio-controller nodes: #gpio-cells = <2>; }; +Usually the GPIO banks in SoCs are ordered, that is there is a dedicated "first +gpio bank". To fix this ordering in the device tree use aliases starting at 0 +(even if the first bank is called "GPIO1" in the hardware reference). +This is necessary/handy to ensure deterministical numbering of GPIOs and GPIO +controllers.
Why is deterministic numbering needed? Rob [1] https://lkml.org/lkml/2016/5/24/470