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

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Date:	Fri, 27 Mar 2015 11:36:25 +0100
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Octavian Purdila <octavian.purdila@...el.com>,
	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 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...)

Sometimes the power-down/up path includes driving pins to
GND using the generic pin config option PIN_CONFIG_OUTPUT to
drive the logic.

For details on this mess where HW designers think that low-power
sleep mode is "GPIO-something" see Documentation/pinctrl.txt
section named "GPIO mode pitfalls". I..e the question is not what
registers are involved and what these are named, but the actual
usecase.

Yours,
Linus Walleij
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