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

Philipp Zabel p.zabel at pengutronix.de
Tue Jul 16 05:49:26 EDT 2013

Hi Shawn,

Am Dienstag, den 16.07.2013, 12:10 +0800 schrieb Shawn Guo:
> On Mon, Jul 15, 2013 at 09:35:52PM -0600, Stephen Warren wrote:
> > > 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.
> I should probably rework the commit log.  But I do not see a problem
> to register gpio-reset driver a little bit earlier.  On the other hand,
> if we reply on deferred probe, many drivers probe could be deferred.
> For example, on my system, the gpio-pca953x on I2C bus works as a GPIO
> controller and provides resets to many board level components.
> Deferring probe of gpio-pca953x on I2C bus means every single probe of
> all these components gets deferred.  IMO, this situation should be
> reasonably avoided.

so you want to have gpio-reset probed at arch_initcall time and you have
gpio-pca953x probed at subsys_initcall time. Won't then all gpio-reset
devices that use gpios on pca953x to reset other peripherals need to be


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