linux-kernel - Re: [PATCH 0/3] drm/gk20a: support for reclocking

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Date:	Thu, 10 Jul 2014 12:43:00 +0300
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Alexandre Courbot <acourbot@...dia.com>
CC:	Ben Skeggs <bskeggs@...hat.com>,
	"nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gnurou@...il.com" <gnurou@...il.com>
Subject: Re: [PATCH 0/3] drm/gk20a: support for reclocking

On Thu, Jul 10, 2014 at 09:34:34AM +0200, Alexandre Courbot wrote:
> This series adds support for reclocking on GK20A. The first two patches touch
> the clock subsystem to allow GK20A to operate, by making the presence of the
> thermal and voltage devices optional, and allowing pstates to be provided
> directly instead of being probed using the BIOS (which Tegra does not have).
> 
> The last patch adds the GK20A clock device. Arguably the clock can be seen as a
> stripped-down version of what is seen on NVE0, however instead of using NVE0
> support has been written from scratch using the ChromeOS kernel as a basis.
> There are several reasons for this:
> 
> - The ChromeOS driver uses a lookup table for the P coefficient which I could
>   not find in the NVE0 driver,
> - Some registers that NVE0 expects to find are not present on GK20A (e.g.
>   0x137120 and 0x137140),
> - Calculation of MNP is done differently from what is performed in
>   nva3_pll_calc(), and it might be interesting to compare the two methods,
> - All the same, the programming sequence is done differently in the ChromeOS
>   driver and NVE0 could possibly benefit from it (?)
> 
> It would be interesting to try and merge both, but for now I prefer to have the
> two coexisting to ensure proper operation on GK20A and besure I don't break
> dGPU support. :)
> 
> Regarding the first patch, one might argue that I could as well add thermal
> and voltage devices to GK20A. The reason this is not done is because these
> currently depend heavily on the presence of a BIOS, and will require a rework
> similar to that done in patch 2 for clocks. I would like to make sure this
> approach is approved because applying it to other subdevs.

I think this should use CCF so we can use pre and post rate change notifiers
to hookup vdd_gpu DVS.

Thanks,

Peter.
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