[PATCH v8] reset: Add driver for gpio-controlled reset pins

On 07/15/2013 07:50 PM, Shawn Guo wrote:

Hi Philipp,

On Thu, May 30, 2013 at 11:09:00AM +0200, Philipp Zabel wrote:

quoted

This driver implements a reset controller device that toggle a gpio
connected to a reset pin of a peripheral IC. The delay between assertion
and de-assertion of the reset signal can be configured via device tree.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Stephen Warren <redacted>

I see this patch is very useful, as GPIOs are widely used to reset
components/devices on board.  But I do not find the patch in v3.11-rc1.
What's your plan about it?

Also, I'm wondering if we should register the driver a little bit
early.  Please see the following patch.  If it makes sense to you,
I can send the patch to you, or you can just quash it into yours.

Shawn

---8<--------

From 2f8ce9e5d6525b98f3828b707458e83fabb39d50 Mon Sep 17 00:00:00 2001
From: Shawn Guo <redacted>
Date: Sun, 14 Jul 2013 20:41:00 +0800
Subject: [PATCH] ENGR00269945: reset: register gpio-reset driver in
 arch_initcall

It's a little bit late to register gpio-reset driver at module_init
time, because gpio-reset provides reset control via gpio for other
devices which are mostly probed at module_init time too.  And it
becomes even worse, when the gpio comes from IO expander on I2C bus,
e.g. pca953x.  In that case, gpio-reset needs to be ready before I2C
bus driver which is generally ready at subsys_initcall time.  Let's
register gpio-reset driver in arch_initcall() to have it ready early
enough.

There's no need for the reset driver to be registered before its users;
the users of the reset GPIO will simply have their probe deferred until
the reset controller is available, and then everything will work out
just fine.

The defer probe mechanism is not used here, because a reset controller
driver should be reasonably registered early than other devices.  More
importantly, defer probe doe not help in some nasty cases, e.g. the
gpio-pca953x device itself needs a reset from gpio-reset driver to start
working.

That should work fine with deferred probe.