[PATCH] unstable/linux-dmabuf: Add 'direct_display' flag

[Marius Vlad]

On 11/14/19 12:20 AM, Drew DeVault wrote:
> Can you elaborate more on non-DRM use-cases? Most compositors are
> already going to use direct scan-out as much as possible, and can make
> reasonably well informed choices about when to do so. For example,
> fullscreen surfaces will generally always be scanned out if possible.

Unfortunately that's only partially correct, the buffer will
(eventually) be scanned out directly, but there's nothing preventing the
compositor to first import into the GPU. That flag assures the client
that (the above) will not never happen.

Really old platforms like i.MX51/i.MX53 have limited bandwidth to
accommodate both video decoding/compositing/rendering and would greatly
benefit from having to ability to bypass the GPU entirely. There's even
lower powered boards which don't have a 3D core at all, but still
capable of video display through a display controller. These are some
potential targets which could benefit from having this available.

> More interesting approaches could include intelligently picking the most
> frequently updated buffers to be placed on planes, or the most optimal
> arrangement for a given combination of pixel formats.
> 
> In addition, the implication that the compositor shouldn't do things
> like letting the user take screenshots when views like this are being
> shown is a chilling effect on non-DRM use-cases, in which taking a
> screenshot is a perfectly reasonable thing to do.

I've seen this raised by Scott, have to admit I'm not aware of the
issues with the screenshots are, nor do I see how this flag would
influence that behaviour. I'll sure take a look to see what's the issue
about it.

> 
> I don't really like the idea of DRM-enabling features being added to
> linux-dmabuf with this level of justification for non-DRM use-cases.
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> 

-- 
Marius Vlad

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