linux-kernel - Re: [PATCH 1/11] ARM: tegra: add function to control the GPU rail clamp

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Date:	Wed, 7 Jan 2015 15:48:08 +0100
From:	Thierry Reding <thierry.reding@...il.com>
To:	Vince Hsu <vinceh@...dia.com>
Cc:	Peter De Schrijver <pdeschrijver@...dia.com>,
	Lucas Stach <dev@...xeye.de>, swarren@...dotorg.org,
	gnurou@...il.com, bskeggs@...hat.com, martin.peres@...e.fr,
	seven@...rod-online.com, samuel.pitoiset@...il.com,
	nouveau@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/11] ARM: tegra: add function to control the GPU rail
 clamp

On Wed, Jan 07, 2015 at 10:28:29PM +0800, Vince Hsu wrote:
> On 04:08:52PM Jan 07, Peter De Schrijver wrote:
> > On Wed, Jan 07, 2015 at 02:27:10PM +0100, Thierry Reding wrote:
> > 
> > > > Yeah. I plan to have the information of all the clock client of the
> > > > partitions and
> > > > the memory clients be defined statically in c source, e.g. pmc-tegra124.c.
> > > > All modules can declare which domain they belong to in DT. One domain can
> > > > be really power gated only when no module is awake. Note the clock clients
> > > > of
> > > > one domain might not equal to the clocks of the module. The reset is not
> > > > either.
> > > > So I don't get the clock and reset from module. How do you think?
> > > 
> > > This whole situation is quite messy. The above sequence basically means
> > > that drivers can't reset hardware modules because otherwise they might
> > > race with the power domain code. It also means that we can't powergate
> > 
> > The powerdomain framework won't call any powergating method as long as a
> > module in the domain is still active. So as long as drivers don't try to
> > reset the hw without having done a pm_runtime_get(), we shouldn't have such
> > a race?
> Agree. And as long as the driver has the correct reset procedure, that should
> be fine to occur between power ungating and gating sequences.
> 
> > 
> > > modules on demand because they might be in the same power domain as one
> > > other module that's still busy.
> > > 
> > 
> > The powerdomain framework keeps track of which modules are active (by hooking
> > into runtime pm) and won't try to shutdown a domain unless all modules are
> > inactive.
> Yeah. By the way, that means we should start supporting runtime pm for all
> the modules to use generic power domain.

Indeed, that'll be a prerequisite before we can merge power domain
support. I do have a couple of local patches that add very rudimentary
runtime PM for various drivers. For starters we could probably just do
the

	pm_runtime_enable(...);
	pm_runtime_get_sync(...)

in the ->probe() and

	pm_runtime_put_sync(...);
	pm_runtime_disable(...);

in the ->remove() callbacks for those drivers. That's by no means
optimal but should get us pretty close to what we do now and still
support the generic power domains.

Thierry

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