From: swarren@wwwdotorg•org (Stephen Warren)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v8] reset: Add driver for gpio-controlled reset pins
Date: Mon, 15 Jul 2013 21:35:52 -0600 [thread overview]
Message-ID: <51E4BF98.8030604@wwwdotorg.org> (raw)
In-Reply-To: <20130716015038.GD28375@S2101-09.ap.freescale.net>
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:
>> 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 <swarren@nvidia•com>
>
> 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 <shawn.guo@linaro•org>
> 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.
next prev parent reply other threads:[~2013-07-16 3:35 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-30 9:09 [PATCH v8] reset: Add driver for gpio-controlled reset pins Philipp Zabel
2013-05-30 10:37 ` Pavel Machek
2013-07-16 1:50 ` Shawn Guo
2013-07-16 3:35 ` Stephen Warren [this message]
2013-07-16 4:10 ` Shawn Guo
2013-07-16 9:49 ` Philipp Zabel
2013-07-16 12:56 ` Shawn Guo
2013-07-16 15:45 ` Stephen Warren
2013-07-17 3:02 ` Shawn Guo
2013-07-17 16:57 ` Stephen Warren
2013-07-17 21:38 ` Pavel Machek
2013-07-17 22:24 ` Stephen Warren
2013-07-18 11:25 ` Pavel Machek
2013-07-18 18:45 ` Olof Johansson
2013-07-19 3:23 ` Shawn Guo
2013-07-19 15:45 ` Stephen Warren
2013-07-22 7:47 ` Shawn Guo
2013-07-26 10:26 ` Philipp Zabel
2013-07-18 22:55 ` Grant Likely
2013-07-18 22:50 ` Grant Likely
2013-07-16 9:59 ` Philipp Zabel
2013-07-16 15:48 ` Stephen Warren
2013-07-16 6:51 ` Shawn Guo
2013-07-16 9:51 ` Philipp Zabel
2013-07-16 12:15 ` Shawn Guo
2013-07-16 15:47 ` Stephen Warren
2013-07-17 3:43 ` Shawn Guo
2013-07-17 7:17 ` Philipp Zabel
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