linux-kernel - Re: [PATCH] IIO: Adds ACPI support for ST gyroscopes

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Date:	Mon, 30 Mar 2015 15:55:14 +0300
From:	Octavian Purdila <octavian.purdila@...el.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Robert Dolca <robert.dolca@...il.com>,
	Robert Dolca <robert.dolca@...el.com>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Denis CIOCCA <denis.ciocca@...com>
Subject: Re: [PATCH] IIO: Adds ACPI support for ST gyroscopes

On Mon, Mar 30, 2015 at 12:52 PM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> On Fri, Mar 27, 2015 at 11:36:25AM +0100, Linus Walleij wrote:
>> On Fri, Mar 27, 2015 at 11:06 AM, Mika Westerberg
>> <mika.westerberg@...ux.intel.com> wrote:
>> > On Thu, Mar 26, 2015 at 06:28:19PM +0200, Octavian Purdila wrote:
>>
>> >> For the sleep case I think the GPIO controller needs to do the pin
>> >> enable and set input direction operation in it's irq_bus_sync_unlock.
>> >
>> > I wonder how DT handles all this? Is it the boot firmware that sets up
>> > the pins accordingly or is there something we are missing?
>>
>> DT systems mostly do not have firmware for power usecases, they
>> handle it all using pin control. I would more say that is a feature of
>> all-SW systems without power-firmware ideas, without ACPI and
>> without PSCI (well PSCI systems do not care about much more
>> than CPU power down in firmware anyway...)
>
> OK, thanks.
>
> In case of ACPI (where firmware does lot more) it is supposed to
> configure pins based on what is connected, if the firmware knows that.
> Due to bugs in the boot firmware that obviously does not happen in all
> cases (like this one).
>

Ah, interesting, I was not aware that the firmware was supposed to do
the pin configuration. In this case I think your patch can be merged
as it is Mika, mine doesn't make sense anymore.

This particular case is special since we did not performed the tests
on a full system that has the component integrated. We instead used
and I2C to USB bridge to which we connected the component and we
loaded the ACPI table dynamically.

> If we want to support requesting IRQ directly through irqchip interface
> on ACPI systems there needs to be some way the GPIO/pinctrl core can use
> to turn the pin as input, GPIO mode.
>
> Octavian's patch does that but not sure if it is good idea for non-ACPI
> systems as they already work. We could also do the same in GPIO/irqchip
> drivers but there is no guarantee for the caller that it is done. IMHO
> safest option is to explictly request the GPIO, turn it input and then
> convert the GPIO to interrupt. That way we know the pin is configured
> just like we expect.
> --
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