Re: [PATCHv3 3/8] drm/omap: add support for manually updated displays

[Daniel Stone]

Hi Tomi,

On 20 April 2018 at 08:09, Tomi Valkeinen <tomi.valkeinen@xxxxxx> wrote:
> It's actually not quite clear to me how manual update displays work with
> DRM...
>
> As far as I see, we have essentially two cases: 1) single buffering,
> where the userspace must set an area in the fb dirty, which then
> triggers the update, 2) multi buffering, which doesn't need fb dirty,
> but just a page flip which triggers the update.
>
> In the 2) case (which I think is the optimal case which all the modern
> apps should use), there's no need for delayed work or any work, and the
> code flow should be very similar to the auto-update model.

Correct. There's been talk (and I think patches?) of adding a
per-plane dirty property, so userspace can as an optimisation inform
the kernel of the area changed between frames. But short of that, a
pageflip needs to trigger a full-plane update, with no dirtyfb
required.

Cheers,
Daniel