On Tue, 16 Apr 2019 10:04:18 -0700 Chia-I Wu <[email protected]> wrote:
> On Tue, Apr 16, 2019 at 2:52 AM Pekka Paalanen <[email protected]> wrote: > > > > On Fri, 12 Apr 2019 10:50:49 -0700 > > Chia-I Wu <[email protected]> wrote: > > > > > Moving the discussion to this patch... > > > > > > This patch clarifies how implicit modifier can be supported, modelling > > > after Weston's behavior. I can see three options > > > > > > 1. DRM_FORMAT_MOD_INVALID means implicit modifier, and is always allowed > > > in buffer creation > > > 2. DRM_FORMAT_MOD_INVALID means implicit modifier, and a modifier event > > > of > > > the value must be sent to indicate buffer creation with implicit modifier > > > is allowed > > > 3. DRM_FORMAT_MOD_INVALID is invalid and there is no implicit modifier > > > support > > > > > > This patch picks option 1. > > > > > > Option 3 makes legacy support impossible, and in turn makes wl_drm > > > deprecation take longer. > > > > > > I've been thinking about moving away from implicit modifier as well so > > > option 2 might be a good compromise. The protocol is also more consistent > > > in that one can create a buffer with a format/modifier pair only when the > > > pair is advertised via the modifier event. > > > > Hi, > > > > yes, allowing to use only combinations of format and modifier that were > > advertised would be nice. We should probably do that when we break the > > protocol ABI the next time if that was not already the case. Until > > then, if compositors have possibly accepted DRM_FORMAT_MOD_INVALID > > without explicitly advertising it, we probably cannot make that illegal > > at the protocol level. This would need a TODO note in the protocol spec > > so we remember to do it during stabilization the latest. > Mutter does not advertise DRM_FORMAT_MOD_INVALID. When a client > creates a buffer with DRM_FORMAT_MOD_INVALID, Mutter passes the > modifier to EGL and let EGL fail the buffer creation. > > Weston always accepts DRM_FORMAT_MOD_INVALID however. It strips the > modifier out so that the drivers do not see the modifier. > > Neither Mesa nor XWayland creates buffers with DRM_FORMAT_MOD_INVALID. > They both fall back to wl_drm when the modifier is > DRM_FORMAT_MOD_INVALID. I guess not a lot of clients, if any, rely on > weston's behavior. Ok, that sounds reasonable. Even more so considering that an implicit modifier only makes sense for self-import on a GPU device, and I have hard time imagining such exports outside of Mesa. Weston might have some test programs, but I wouldn't consider those blockers. If necessary, they can be fixed at the same time Weston is. Thanks, pq
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