Messages in this thread |  | | Date | Wed, 22 Oct 2014 11:10:44 +0300 | From | Mika Westerberg <> | Subject | Re: GPIO bindings guidelines (Was: Re: [PATCH v5 10/12] gpio: Support for unified device properties interface) |
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On Tue, Oct 21, 2014 at 09:54:45AM +0200, Arnd Bergmann wrote: > On Tuesday 21 October 2014 14:14:02 Alexandre Courbot wrote: > > > > > > We have enforced naming things for the dmaengine binding, which has > > > just led to everyone calling things "rx" and "tx". My fear is that > > > if we start to enforce giving a name, we'd end up with lots of > > > drivers that use a "gpio-gpios" property or something silly. > > > > Checking the bindings is also part of the review process. Things > > like "gpio-gpios" should simply not be accepted to begin with. > > > > This sounds like a good chance to finally land some guidelines > > regarding GPIO bindings. Let's summarize the situation: > > - GPIO bindings can be defined using both DT and ACPI (both interfaces > > nicely abstracted by the interface introduced by this series) > > - Both firmware interfaces support indexed GPIOs > > - Both firmware interfaces support named GPIO properties, with an > > optional index (can we absolutely take this for granted on ACPI now?) > > The developers working on it have said that they definitely want to > be compatible with the existing bindings, so the answer to your question > is yes.
One thing to consider still is that we have plenty of existing ACPI code out there where _DSD is not used but instead we rely on the index. An example would be rfkill-gpio.c driver:
gpio = devm_gpiod_get_index(&pdev->dev, "reset", 0); if (!IS_ERR(gpio)) { ... }
gpio = devm_gpiod_get_index(&pdev->dev, "shutdown", 1); if (!IS_ERR(gpio)) { ... }
It expects that GPIOs returned from _CRS are in specific order. Since we can't change these existing ACPI tables, we must support them somehow.
This patch series handles it so that:
1) If we can't find given property (e.g "reset-gpios" or "shutdown-gpios") the index above will refer directly to the GPIO resource returned from _CRS.
2) If the property is found we ignore index and take it from the property instead.
This has the drawback that we cannot support this:
Package () { "reset-gpios", Package () { ^GPIO, 0, 0, 0, ^GPIO, 1, 0, 0}} ^^^^^^^^^^^^^^ So the second entry in the above is not accessible using gpiod_get_index() and the reason is that we want to support the existing and new ACPI tables where _DSD is not being used.
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