linux-kernel - Re: Pinctrl hogging

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Message-ID: <CACRpkdZxsdgMf+iAcMv1gC6p=JFg0dpZ=UW2TksKZhhOwA6G+A@mail.gmail.com>
Date:	Thu, 28 Jul 2016 18:12:58 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	noman pouigt <variksla@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: Pinctrl hogging

On Thu, Jul 21, 2016 at 6:21 PM, noman pouigt <variksla@...il.com> wrote:

> Is there any way to configure default settings for some of the gpios
> eventhough there is no one driving them?

There are gpio hogs but I don't remember which kernel we
introduced them in. Please keep in sync with upstream.
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/Documentation/devicetree/bindings/gpio/gpio.txt?id=6b516a1093006a39368dd11a5396be5bb00c99df

> I am also trying to configure
> some of the gpios as irq lines using just the device tree without
> writing any device driver for it as it will be used by userspace.

I don't recommend randomly using GPIO from userspace. Have you read:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/gpio/drivers-on-gpio.txt

If you still have a valid usecase for userspace GPIO, consider
getting the latest v4.8 kernel when it's out in some two months
and use the new chardev ABI that I just merged. The sysfs
ABI is not good, and that is why it has been obsolted.

We can name lines with gpio-line-names =""; in device tree and
there are example tools for how to use GPIOs from userspace
in a proper way:
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/tools/gpio

> Just to workaround this problem I have created a dummy driver
> specifically for this purpose. Is there any better way?

Keeping in touch with upstream and driving changes upstream is
always the best solution.

Yours,
Linus Walleij