Re: [PATCH v3 1/1] pinctrl: add Intel BayTrail GPIO/pinctrl support

From: Mathias Nyman
Date: Wed Jun 19 2013 - 06:24:27 EST

On 06/18/2013 06:17 PM, Linus Walleij wrote:
On Tue, Jun 18, 2013 at 1:33 PM, Mathias Nyman
<mathias.nyman@xxxxxxxxxxxxxxx> wrote:

Add support for gpio on Intel BayTrail platforms. BayTrail supports 3 banks
of gpios called SCORE, NCORE ans SUS with 102, 28 and 44 gpio pins.
Supports gpio interrupts and ACPI gpio events

Pins may be muxed to alternate function instead of gpio by firmware.
This driver does not touch the pin muxing and expect firmare
to set pin muxing and pullup/down properties properly.

Signed-off-by: Mathias Nyman<mathias.nyman@xxxxxxxxxxxxxxx>

I have a feeling this driver will evolve quite a bit and eventually
register a pure pinctrl interface as well (currently it's only using
the ranges as some data container...)

Anyway, it's a good starting point and obviously (I guess?)
gets your hardware up an ticking, so let's take this as a
starting point.

So patch applied.

Thanks, much appreciated.
We'll see how it evolves.

This thing only seems to use gpiolib-acpi.c for the basic
device matching and IRQ handling backend, is that correct?

It only uses gpiolib-acpi.c for handling GPIO-signaled ACPI Events,
which are like SCI events on hardware reduced ACPI platforms.

Basically It's ACPI saying "I have a firmware method that needs to be run if a certain gpio is triggered, please do that for me"

So the acpi_gpiochip_request_interrupts() registers interrupt handlers which call ACPI firmware methods for those gpio interrupts.

Otherwise gpiolib-acpi.c is useful for other device drivers to translate ACPI gpio resource numbers to linux gpio numbers. In ACPI tables the gpio resource numbers are per controller and zero based.

What I'm thinking of moving forward is that I have seen
ACPI fragments with things like "PullUp" etc, which is pinctrl
domain, so we may come to need some generic ACPI helpers
inside drivers/pinctrl as well sooner or later.

Probably yes, I'm not an expert on ACPI (or pinctrl), but ACPI5 added the GpioInt and GpioIo resources for devices. GpioInt resource descriptor has the follwing arguments: GpioInt(EdgeLevel, ActiveLevel, Shared, PinConfig, DebounceTimeout, ResourceSource,
esourceSourceIndex, ResourceUsage, DescriptorName, VendorData) {PinList}

Where the PinConfig argument can be PullDefault, PullUp, PullDown, PullNone or some vendor specific value.

ResourceSource tells which gpio controller the pin belongs to.

Right now drivers only have helpers for translating the ACPI gpio pin number to linux gpio number.

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