linux-kernel - Re: [5/5] ARM: tegra: jetson-tk1: enable GK20A GPU

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Message-ID: <20140925164109.GA30382@ulmo>
Date:	Thu, 25 Sep 2014 18:41:11 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Sjoerd Simons <sjoerd@...n.net>,
	Alexandre Courbot <acourbot@...dia.com>,
	Ben Skeggs <bskeggs@...hat.com>, nouveau@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org, gnurou@...il.com
Subject: Re: [5/5] ARM: tegra: jetson-tk1: enable GK20A GPU

On Thu, Sep 25, 2014 at 09:48:01AM -0600, Stephen Warren wrote:
> On 09/25/2014 07:27 AM, Sjoerd Simons wrote:
> >Playing a bit with todays linux-next on my jetson, it seems this patch is
> >still required for enabling the GPU. Is there anything blocking it (firmware
> >not available yet in liux-firmware?)
> 
> I think initially I was waiting for the DRM patch "drm/nouvea: support for
> probing platform devices" to be applied, but it looks like that's been
> applied already, so only patches 4 and 5 in this series are still
> outstanding.
> 
> Alex, wasn't there also some issue where the VPR register had to be
> programmed, and if it wasn't there'd be a hang when the GPU registers were
> touched? If we've added code to Nouveau/tegradrm to detect that and avoid
> the problem, then I guess we can commit these last two patches for 3.19. A
> resend after the 3.18 merge window might help.

A patch that programs VPR was merged into U-Boot (though I don't think
it's made it into master yet). I'm not sure we can reasonably check for
that in Nouveau, given that the register is somewhere completely
unrelated. In fact I think the U-Boot patch was triggered by some
discussion about how to solve this and it was decided that it shouldn't
be done in the kernel, but U-Boot should set it up.

That said, perhaps one solution would be to make U-Boot enable the gk20a
device if it's set up the VPR and disable it otherwise?

Thierry

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