Maxime Ripard [off-list ref] wrote on Wed [2014-Oct-29 11:45:59 +0100]:

Hi,

On Tue, Oct 21, 2014 at 03:09:58PM -0500, Benoit Parrot wrote:

quoted

Based on Boris Brezillion work this is a reworked patch
of his initial GPIO hogging mechanism.
This patch provides a way to initally configure specific GPIO
when the gpio controller is probe.

The actual DT scanning to collect the GPIO specific data is performed
as part of the gpiochip_add().

The purpose of this is to allows specific GPIOs to be configured
without any driver specific code.
This particularly usueful because board design are getting
increassingly complex and given SoC pins can now have upward
of 10 mux values a lot of connections are now dependent on
external IO muxes to switch various modes and combination.

Specific drivers should not necessarily need to be aware of
what accounts to a specific board implementation. This board level
"description" should be best kept as part of the dts file.

Signed-off-by: Benoit Parrot <redacted>

I've been thinking about this for quite some time, it's good to see
some progress on that :)

However, I have a slightly different use case for it: the Allwinner
SoCs have a vdd pin coming in for every gpio bank. Nothing out of the
ordinary so far, except that some of the boards are using a
GPIO-controlled regulator to feed another bank vdd. That obviously
causes a chicken-egg issue, since for the gpio-regulator driver to
probe, it needs to gpio driver, and for the gpio driver to probe, it
needs the regulator driver.

Unless the gpio controlling the vdd pin is from the same bank your trying to power up
I do not see the issue here.

In this patch the gpio-hogs are setup as part of the gpio-controller probe function.

I was thinking of solving this by enforcing gpio hogs, in order to
have the gpio driver loading, grabing its gpios setting them to the
right value to enable the current to flow in, and then let the
regulator driver probe later on.

I don't think it's possible with your current code, would it be
something worth considering, or would someone have a better solution?

Unless I am missing something, this should work.

Maxime
-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

Regards,
Benoit