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

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Message-ID: <53BE61D9.4020202@nvidia.com>
Date:	Thu, 10 Jul 2014 12:50:17 +0300
From:	Mikko Perttunen <mperttunen@...dia.com>
To:	Alexandre Courbot <acourbot@...dia.com>,
	Ben Skeggs <bskeggs@...hat.com>
CC:	"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

Does GK20A itself have any kind of thermal protection capabilities? 
Upstream SOCTHERM support is not yet available (though I have a driver 
in my tree), so we are thinking of disabling CPU DVFS on boards that 
don't have always-on active cooling for now. Same might be necessary for 
GPU as well.

On 10/07/14 10:34, 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.
>
> Alexandre Courbot (3):
>    drm/nouveau/clk: make therm and volt devices optional
>    drm/nouveau/clk: support for non-BIOS pstates
>    drm/gk20a: reclocking support
>
>   drivers/gpu/drm/nouveau/Makefile                   |   1 +
>   drivers/gpu/drm/nouveau/core/engine/device/nve0.c  |   1 +
>   .../gpu/drm/nouveau/core/include/subdev/clock.h    |   9 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/base.c   |  52 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/gk20a.c  | 670 +++++++++++++++++++++
>   drivers/gpu/drm/nouveau/core/subdev/clock/nv04.c   |   4 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nv40.c   |   4 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nv50.c   |   2 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nva3.c   |   4 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nvaa.c   |   4 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nvc0.c   |   4 +-
>   drivers/gpu/drm/nouveau/core/subdev/clock/nve0.c   |   4 +-
>   12 files changed, 725 insertions(+), 34 deletions(-)
>   create mode 100644 drivers/gpu/drm/nouveau/core/subdev/clock/gk20a.c
>
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