Re: [PATCH 1/2] x86, gpio: Increase ARCH_NR_GPIOs to 512

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Sep 8, 2014 at 1:47 PM, Mika Westerberg
<mika.westerberg@xxxxxxxxxxxxxxx> wrote:

> Some newer Intel SoCs like Braswell already have more than 256 GPIOs
> available so the default limit is exceeded. In order to support these add
> back the custom GPIO header with limit of 512 GPIOs for x86.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>

Argh! This is the kind of stuff I want to get rid of ....

Preferably gpio should be a subsystem without a lot of hooks all over
the place with arch-specific modifications for this and that, including
the max number of GPIOs.

I would actually prefer if you bump the value in
include/asm-generic/gpio.h to 512 over this.

But better still, now that we have descriptors etc would be to define
some new per-arch selectable config option like
CONFIG_ONLY_DYNAMIC_GPIO that changes the GPIO
core to use something like a radix tree to store and retrieve
descriptors.

I.e. in drivers/gpio/gpiolib.c get rid of this:
static struct gpio_desc gpio_desc[ARCH_NR_GPIOS];

Replace it with a radix tree of descriptors.

This however makes it *impossible* to use things like desc_to_gpio()
and/or gpio_to_desc() so the code has to be augmented all over the
place to avoid any uses of GPIO numbers on that architecture,
but I am sure it *can* be done on pure ACPI or device tree
systems, and that's what we should aim for.

Comments?

Yours,
Linus Walleij
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