linux-kernel - Re: [PATCH v5 09/11] drm/tegra: Reset the SOR on probe

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Date:	Tue, 3 Mar 2015 16:59:26 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Simon Glass <sjg@...omium.org>
Cc:	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Javier Martinez Canillas <javier.martinez@...labora.co.uk>,
	Dylan Reid <dgreid@...omium.org>,
	Andrew Bresticker <abrestic@...omium.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Terje Bergström <tbergstrom@...dia.com>,
	David Airlie <airlied@...ux.ie>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 09/11] drm/tegra: Reset the SOR on probe

On Tue, Mar 3, 2015 at 12:46 AM, Simon Glass <sjg@...omium.org> wrote:
> Hi,
>
> On 2 March 2015 at 01:41, Alexandre Courbot <gnurou@...il.com> wrote:
>>
>> On Thu, Feb 12, 2015 at 5:51 PM, Tomeu Vizoso
>> <tomeu.vizoso@...labora.com> wrote:
>> > As there isn't a way for the firmware on the Nyan chromebooks to hand
>> > over the display to the kernel.
>>
>> Could this have a side-effect on models for which the firmware *does*
>> hand over the display to the kernel? E.g. temporary glitch or black
>> screen?
>>
>> This is probably ok though, as such a handing over would need to be
>> documented in the firmware/kernel command line, and could thus be
>> caught to disable that code block if needed.
>
> Is there a general way in which this hand-over is done, e.g. with a
> device tree binding?

simple-framebuffer has bindings that describe a framebuffer handed
over by the firmware, and they look like the right way to describe
this. simplefb however is a framebuffer driver - a DRM driver would
need to seamlessly take over the display at some point and disable
simplefb. I don't know if this is possible at the moment.

Or maybe the DRM framework could look for a simple-framebuffer
compatible node, extract the framebuffer information, and pass it to
DRM drivers at probe time. That supposes a kernel in which
simple-framebuffer is not compiled in to prevent it from taking over
the display.
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