[alsa-devel] [PATCH 2/4] ASoC: s3c64xx/smartq: use dynamic registration

[Alexandre Courbot]

On Tue, Jul 15, 2014 at 4:19 PM, Arnd Bergmann <arnd at arndb.de> wrote:
> On Monday 14 July 2014 19:36:24 Mark Brown wrote:
>> On Mon, Jul 14, 2014 at 08:23:55PM +0200, Arnd Bergmann wrote:
>> > On Monday 14 July 2014 18:18:12 Lars-Peter Clausen wrote:
>>
>> > > Yes. But now that you say it the gpiod_direction_output() call is missing
>> > > from this patch.
>>
>> > I'm lost now. The GPIO_ACTIVE_HIGH I added comes from Documentation/gpio/board.txt
>> > and as Linus Walleij explained to me the other day, the lookup is supposed
>> > to replace devm_gpio_request_one(), which in turn replaced both the
>> > gpio_request and the gpio_direction_output(). Do I need to put the
>> > gpiod_direction_output() back or is there another interface for that when
>> > registering the board gpios?
>>
>> Indeed.  If you *do* need an explicit _output() then that sounds to me
>> like we either need a gpiod_get_one() or an extension to the table,
>> looking at the code it seems like this is indeed the case.  We can set
>> if the GPIO is active high/low, or open source/drain but there's no flag
>> for the initial state.
>
> (adding Alexandre and the gpio list)
>
> GPIO people: any guidance on how a board file should set a gpio to
> output/default-high in a GPIO_LOOKUP() table to replace a
> devm_gpio_request_one() call in a device driver with devm_gpiod_get()?
> Do we need to add an interface extension to do this, e.g. passing
> GPIOF_OUT_INIT_HIGH as the flags rather than GPIO_ACTIVE_HIGH?

The way I see it, GPIO mappings (whether they are done using the
lookup tables, DT, or ACPI) should only care about details that are
relevant to the device layout and that should be abstracted to the
driver (e.g. whether the GPIO is active low or open drain) so drivers
do not need to check X conditions every time they want to drive the
GPIO.

Direction and initial value, on the other hand, are clearly properties
that ought to be set by the driver itself. Thus my expectation here
would be that the driver sets the GPIO direction and initial value as
soon as it gets it using gpiod_direction_output(). In other words,
there is no replacement for gpio_request_one() with the gpiod
interface. Is there any use-case that cannot be covered by calling
gpiod_direction_output() right after gpiod_get()? AFAICT this is what
gpio_request_one() was doing anyway.