[Mesa-dev] [RFC] gbm: wire up fence extension

[Rob Clark]

On Thu, Aug 18, 2016 at 8:45 AM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
> On 16 August 2016 at 18:01, Rob Clark <robdclark at gmail.com> wrote:
>> I noticed that fence extension wasn't exposed for drm/gbm, which sort
>> of defeats the purpose of using fence fd's for synchronizing rendering
>> and atomic pageflip.
>>
> Afaict this is a slightly more complete version of Philipp's patch.
>
> While my earlier suggestion still stands, I should have mentioned that
> it's not a show stopper for this patch.
> Namely: we really want a way to check and bail out on ABI mismatch
> between libEGL and libgbm.

btw, I dug up Philipp's original patch/thread..  I didn't realize that
someone had already done this (would have saved me some time ;-))

As far as ABI mismatch, we don't currently ship libEGL/libgbm
separately.  And there doesn't appear to be any versioning scheme so
far.  (Although if we do split out libgbm from mesa, that would be a
good thing to add.)

So I'm inclined to punt on the version check (and actually not
entirely sure it is even possible).

BR,
-R

>> I suppose that somewhere or other, there needs to be a similar change
>> to .../state_trackers/dri/dri2.c to avoid breaking things on i965.
> Kind of ... see below.
>
>
>> ---
>>  src/egl/drivers/dri2/platform_drm.c   | 1 +
>>  src/gallium/state_trackers/dri/dri2.c | 1 +
>>  src/gbm/backends/dri/gbm_dri.c        | 1 +
>>  src/gbm/backends/dri/gbm_driint.h     | 1 +
>>  4 files changed, 4 insertions(+)
>>
>> diff --git a/src/egl/drivers/dri2/platform_drm.c b/src/egl/drivers/dri2/platform_drm.c
>> index 1ce282f..7bea8e1 100644
>> --- a/src/egl/drivers/dri2/platform_drm.c
>> +++ b/src/egl/drivers/dri2/platform_drm.c
>> @@ -645,6 +645,7 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
>>     dri2_dpy->dri_screen = dri2_dpy->gbm_dri->screen;
>>     dri2_dpy->core = dri2_dpy->gbm_dri->core;
>>     dri2_dpy->dri2 = dri2_dpy->gbm_dri->dri2;
>> +   dri2_dpy->fence = dri2_dpy->gbm_dri->fence;
> Nice catch. Philipp's patch was missing this hunk, thus one could not
> have really used the fence extension from EGL.
>
>>     dri2_dpy->image = dri2_dpy->gbm_dri->image;
>>     dri2_dpy->flush = dri2_dpy->gbm_dri->flush;
>>     dri2_dpy->swrast = dri2_dpy->gbm_dri->swrast;
>> diff --git a/src/gallium/state_trackers/dri/dri2.c b/src/gallium/state_trackers/dri/dri2.c
>> index 75d740b..8ad8701 100644
>> --- a/src/gallium/state_trackers/dri/dri2.c
>> +++ b/src/gallium/state_trackers/dri/dri2.c
>> @@ -2042,6 +2042,7 @@ const __DRIextension *galliumdrm_driver_extensions[] = {
>>      &driImageDriverExtension.base,
>>      &driDRI2Extension.base,
>>      &gallium_config_options.base,
>> +    &dri2FenceExtension.base,
> While things are a bit confusing I think this shouldn't be here, and
> thus there's no 'missing' i965 hunk.
>
> galliumdrm_driver_extensions are the "core" extensions which among
> other are responsible for:
>  - setting up the screen (which itself sets up the screen extensions)
>  - query screen extensions
>
> As a simple test - both gallium and i965 already expose the fence
> extension and it seems to be working fine afaict.
>
> Regards,
> Emil