Advertising supported Dmabuf modifiers of DRM device

[Daniel Stone]

Hi Emre,

On Fri, 27 Jul 2018 at 07:44, Ucan, Emre (ADITG/ESB)
<eucan at de.adit-jv.com> wrote:
> IMO, entire point of having wayland surfaces and buffers to use them for display scanout.
>
> If an application does not want to display its rendered content, it can use surfaceless context or render to texture etc.

Sure, and where possible we should use the overlay! But if there are
more Wayland surface views than there are overlay planes, it is not
possible to show all them on the overlay. In that case, we should fall
back to the most efficient method, i.e. what is best for the GPU.

Taking i.MX6 as an example - if we know we can never show at least one
view on an overlay (because it's transformed, or too many views, etc),
then we should not waste any time and energy having that surface do a
linear resolve. We can just skip this step and have the GPU output
tiled and then consume tiled during composition.

> Furthermore, we don’t have information in weston about content producing device.
> If an application wants to render with gpu, it should be responsibility of the application to query and use gpu friendly modifiers.
> We can provide them a list of scanout friendly modifiers which application can use. Then, application should choose a format which would work for rendering and scanout.

Right, but again this may lead us to lose performance if the
application tries to find the lowest-common-denominator layout, when
it doesn't need to. Hence the suggestion for the compositor suggesting
the most appropriate sets of modifiers to clients depending on the
situation.

Cheers,
Daniel