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

[Emil Velikov]

On 18 August 2016 at 14:12, Rob Clark <robdclark at gmail.com> wrote:
> 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.
>>
>>> 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.
>
> Ok, in that case I think we need this hunk squashed in (but untested so far):
>
> --------
> diff --git a/src/gbm/backends/dri/gbm_dri.c b/src/gbm/backends/dri/gbm_dri.c
> index d4602d1..3cd8783 100644
> --- a/src/gbm/backends/dri/gbm_dri.c
> +++ b/src/gbm/backends/dri/gbm_dri.c
> @@ -244,13 +244,13 @@ struct dri_extension_match {
>  static struct dri_extension_match dri_core_extensions[] = {
>     { __DRI2_FLUSH, 1, offsetof(struct gbm_dri_device, flush) },
>     { __DRI_IMAGE, 1, offsetof(struct gbm_dri_device, image) },
> +   { __DRI2_FENCE, 2, offsetof(struct gbm_dri_device, fence) },
>     { NULL, 0, 0 }
>  };
>
>  static struct dri_extension_match gbm_dri_device_extensions[] = {
>     { __DRI_CORE, 1, offsetof(struct gbm_dri_device, core) },
>     { __DRI_DRI2, 1, offsetof(struct gbm_dri_device, dri2) },
> -   { __DRI2_FENCE, 2, offsetof(struct gbm_dri_device, fence) },
>     { NULL, 0, 0 }
>  };
>  --------
>
Yes you're correct - we'll need to expose it (why did I read
DRI2_FLUSH as DRI2_FENCE?).

Adding it to the array makes it compulsory, due to the nature of
dri_bind_extensions(). We could do that but it'll break all the
classic drivers but i965.

Something like the egl handling would be better:

   for (i = 0; extensions[i]; i++) {
      if (strcmp(extensions[i]->name, __DRI2_FENCE) == 0)
         dri2_dpy->fence = (__DRI2fenceExtension *) extensions[i];
   }


-Emil