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

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Message-ID: <20150330133307.GE1524@lahna.fi.intel.com>
Date:	Mon, 30 Mar 2015 16:33:07 +0300
From:	Mika Westerberg <mika.westerberg@...ux.intel.com>
To:	Octavian Purdila <octavian.purdila@...el.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 03:55:14PM +0300, Octavian Purdila wrote:
> 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.

Unfortunately because of bugs we can't rely that the firmware (BIOS)
gets those always right :-(

> 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.

Regardless of how did the device appear this always works:

  1) request the GPIO (with GPIOD_IN)
  2) convert it to IRQ using gpiod_to_irq()

Since we cannot be sure that the firmware has configured the pin
properly, rather than adding automatic IRQ <-> GPIO translation for ACPI
GpioInt I think we are better off if drivers explictly request their
GPIOs and configure them as needed.
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