linux-kernel - Re: [PATCH] gpiolib-acpi: introduce acpi_get_gpio_by

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Date:	Thu, 4 Apr 2013 12:57:16 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Benjamin Tissoires <benjamin.tissoires@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	Grant Likely <grant.likely@...retlab.ca>,
	Linus Walleij <linus.walleij@...aro.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH] gpiolib-acpi: introduce acpi_get_gpio_by_index() helper

On Thu, Apr 04, 2013 at 11:42:11AM +0200, Benjamin Tissoires wrote:
> On Thu, Apr 4, 2013 at 11:38 AM, Mika Westerberg
> <mika.westerberg@...ux.intel.com> wrote:
> > On Thu, Apr 04, 2013 at 11:19:53AM +0200, Benjamin Tissoires wrote:
> >> Hi Mika,
> >>
> >> On Wed, Apr 3, 2013 at 12:56 PM, Mika Westerberg
> >> <mika.westerberg@...ux.intel.com> wrote:
> >> > Instead of open-coding ACPI GPIO resource lookup in each driver, we provide
> >> > a helper function analogous to Device Tree version that allows drivers to
> >> > specify which GPIO resource they are interested (using an index to the GPIO
> >> > resources). The function then finds out the correct resource, translates
> >> > the ACPI GPIO number to the corresponding Linux GPIO number and returns
> >> > that.
> >> >
> >> > Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> >> > ---
> >> >  Documentation/acpi/enumeration.txt |   32 ++++++++++++++-
> >> >  drivers/gpio/gpiolib-acpi.c        |   77 ++++++++++++++++++++++++++++++++++++
> >> >  include/linux/acpi_gpio.h          |   17 ++++++++
> >> >  3 files changed, 125 insertions(+), 1 deletion(-)
> >> >
> >> > diff --git a/Documentation/acpi/enumeration.txt b/Documentation/acpi/enumeration.txt
> >> > index 94a6561..b0d5410 100644
> >> > --- a/Documentation/acpi/enumeration.txt
> >> > +++ b/Documentation/acpi/enumeration.txt
> >> > @@ -199,6 +199,8 @@ the device to the driver. For example:
> >> >         {
> >> >                 Name (SBUF, ResourceTemplate()
> >> >                 {
> >> > +                       ...
> >> > +                       // Used to power on/off the device
> >> >                         GpioIo (Exclusive, PullDefault, 0x0000, 0x0000,
> >> >                                 IoRestrictionOutputOnly, "\\_SB.PCI0.GPI0",
> >> >                                 0x00, ResourceConsumer,,)
> >> > @@ -206,10 +208,20 @@ the device to the driver. For example:
> >> >                                 // Pin List
> >> >                                 0x0055
> >> >                         }
> >> > +
> >> > +                       // Interrupt for the device
> >> > +                       GpioInt (Edge, ActiveHigh, ExclusiveAndWake, PullNone,
> >> > +                                0x0000, "\\_SB.PCI0.GPI0", 0x00, ResourceConsumer,,)
> >>
> >> Sorry for coming late in the GPIO ACPI discussion, but when I see this
> >> documentation, I wonder:
> >> wouldn't it be feasible to find the correct GPIO by its type? Here, we
> >> have a GpioIo and a GpioInt, and I bet this would be sometime more
> >> useful to request the first GpioInt without knowing the correct order
> >> of declarations.
> >
> > Why not. But then again you can always check the type returned in the
> > acpi_gpio_info structure and pick the first GpioInt (if you have multiple
> > GPIO resources).
> >
> >> It may be feasible by walking the tree, but a helper would be of great
> >> help (thinking at i2c-hid here, which can not rely on indexes in the
> >> DSDT).
> >
> > Well, index is the only thing we can rely on unfortunately. There's nothing
> > like names or anything like that.
> >
> > What I've seen from ACPI enumerated i2c-hid devices there is only one GPIO
> > resource (GpioInt) declared.
> 
> Ok, thanks for the answer. I guess the idea would be to pick the index
> 0, check the type, and try indexes 1 or 2 if it's not GpioInt. I bet
> there will be devices with more than one Gpio as most of I2C input
> device have a reset line (except if Microsoft forces them not to have
> one).

One option is to provide acpi_get_gpio_all() that returns all GPIOs and
their corresponding types. That should allow clients like i2c-hid to find
the right GPIO (I'm hoping that there will be only one GpioInt associated
with these devices).
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