Nouveau - Jan 2015 - [PATCH 1/11] ARM: tegra: add function to control the GPU rail clamp

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

Peter.

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.

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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