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

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Message-ID: <20150106135110.GA18076@nvidia.com>
Date:	Tue, 6 Jan 2015 21:51:11 +0800
From:	Vince Hsu <vinceh@...dia.com>
To:	Thierry Reding <thierry.reding@...il.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 02:29:32PM Jan 06, Thierry Reding wrote:
> * PGP Signed by an unknown key
> 
> On Tue, Jan 06, 2015 at 08:03:03PM +0800, Vince Hsu wrote:
> > On 01/06/2015 07:15 PM, Thierry Reding wrote:
> > >> Old Signed by an unknown key
> > >
> > >On Tue, Jan 06, 2015 at 10:11:41AM +0800, Vince Hsu wrote:
> > >>On 01/05/2015 11:09 PM, Thierry Reding wrote:
> > >>>>Old Signed by an unknown key
> > >>>On Thu, Dec 25, 2014 at 10:28:08AM +0800, Vince Hsu wrote:
> > >>>>On 12/24/2014 09:16 PM, Lucas Stach wrote:
> > >>>>>Am Dienstag, den 23.12.2014, 18:39 +0800 schrieb Vince Hsu:
> > >>>>>>The Tegra124 and later Tegra SoCs have a sepatate rail gating register
> > >>>>>>to enable/disable the clamp. The original function
> > >>>>>>tegra_powergate_remove_clamping() is not sufficient for the enable
> > >>>>>>function. So add a new function which is dedicated to the GPU rail
> > >>>>>>gating. Also don't refer to the powergate ID since the GPU ID makes no
> > >>>>>>sense here.
> > >>>>>>
> > >>>>>>Signed-off-by: Vince Hsu <vinceh@...dia.com>
> > >>>>>To be honest I don't see the point of this patch.
> > >>>>>You are bloating the PMC interface by introducing another exported
> > >>>>>function that does nothing different than what the current function
> > >>>>>already does.
> > >>>>>
> > >>>>>If you need a way to assert the clamp I would have expected you to
> > >>>>>introduce a common function to do this for all power partitions.
> > >>>>I thought about adding an tegra_powergate_assert_clamping(), but that
> > >>>>doesn't make sense to all the power partitions except GPU. Note the
> > >>>>difference in TRM. Any suggestion for the common function?
> > >>>I don't think extending the powergate API is useful at this point. We've
> > >>>long had an open TODO item to replace this with a generic API. I did
> > >>>some prototyping a while ago to use generic power domains for this, that
> > >>>way all the details and dependencies between the partitions could be
> > >>>properly modeled.
> > >>>
> > >>>Can you take a look at my staging/powergate branch here:
> > >>>
> > >>>	https://github.com/thierryreding/linux/commits/staging/powergate
> > >>>
> > >>>and see if you can use that instead? The idea is to completely hide the
> > >>>details of power partitions from drivers and use runtime PM instead.
> > >>You generic power domains work is exactly what we want for powergate
> > >>eventually. :) I recall we used your prototyping in somewhere internal tree.
> > >>We have to add more to complete it though, e.g. power domain dependency, mc
> > >>flush, and clamping register difference like this patch does.
> > >>
> > >>But I have a question here. Since the GK20A is not powered on/off by the PMC
> > >>except the clamping control, and GK20A has its own power rail, do we really
> > >>want to hide the power sequence in the generic powergate code? We still have
> > >>to control the voltage level in the GK20A driver through the regulator
> > >>framework. It seems weird to me if we put the regulator_{enable|disable}
> > >>somewhere other than the GK20A driver.
> > >I think we want both. The power domain to control the power partition
> > >and the regulator in the gk20a driver for the voltage control.
> > Do you mean excluding the power sequence of GK20A from the generic power
> > domain?
> 
> No, what I mean is move the power gating into the PMC driver as part of
> the generic power domain implementation. At the same time, keep the
> control of the regulator within the gk20a driver. That way we can use
> runtime PM to control the powergating but we can still control the GPU
> voltage within Nouveau.
Okay. Do you insist to introduce the generic power domain at this moment?
If so, I can try to continue your previous work and rebase this series on
that. That might take some time though.

Thanks,
Vince

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