Re: [RFC 4/4] drm: Add NVIDIA Tegra support

[Thierry Reding <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org>]

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* Alex Deucher wrote:
> On Thu, Apr 12, 2012 at 5:33 AM, Thierry Reding
> <thierry.reding-RM9K5IK7kjKj5M59NBduVrNAH6kLmebB@public.gmane.org> wrote:
> > In other words I would like to use the Tegra hardware to render content into
> > a framebuffer (using potentially the 3D engine or HW accelerated video
> > decoding blocks) but display that framebuffer with a CRTC registered by a
> > different driver (perhaps provided by a PCIe or USB device).
> >
> > I think such a setup would be possible if the CRTC registration can be
> > decoupled from the DRM driver. Perhaps sdrm even supports that already?
> 
> You should be able to do something like that already with dma_buf and
> the drm prime infrastructure.  There's even a drm driver for the udl
> USB framebuffer devices.

Using DRM PRIME requires user-space to be involved. I was thinking more along
the lines of allowing a dumb DRM driver that only provides a CRTC to register
with another driver so that it shows up as an output for the latter DRM
device.

Then again, having user-space control this may be more flexible. Performance-
wise both should be about the same, right? What I don't quite understand yet
is how the DMABUF would be synchronized on both ends. Is there some infra-
structure to account for it or would I have to export two buffers and flip
them during the vblank of the "consumer"?

Thierry

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