On Tue, Oct 21, 2014 at 09:54:45AM +0200, Arnd Bergmann wrote:

On Tuesday 21 October 2014 14:14:02 Alexandre Courbot wrote:

quoted

quoted

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.