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

[Emil Velikov]

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.

> 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