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

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Message-ID: <20150107142828.GB7392@nvidia.com>
Date:	Wed, 7 Jan 2015 22:28:29 +0800
From:	Vince Hsu <vinceh@...dia.com>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
CC:	Thierry Reding <thierry.reding@...il.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 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.

Thanks,
Vince

> 
> > How would we handle a situation where a hardware module hangs and we can
> > only get it back via a reset?
> > 
> 
> Cheers,
> 
> Peter.
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