[Mesa-dev] Removing GRALLOC_MODULE_PERFORM_GET_DRM_FD

[Tomasz Figa]

Hi Stefan,

On Thu, Mar 22, 2018 at 8:42 AM, Stefan Schake <stschake at gmail.com> wrote:
> Hey Robert,
>
> On Wed, Mar 21, 2018 at 4:16 PM, Robert Foss <robert.foss at collabora.com> wrote:
>> Hey,
>>
>> I've started looking into removing the gralloc method
>> GRALLOC_MODULE_PERFORM_GET_DRM_FD.
>>
>> The issues around this seems to be two parts:
>> 1) Finding the right device to open
>> 2) Sharing the device between components
>>
>> Sharing the device between components
>> -------------------------------------
>>
>> Currently the device is used by drm_hwc, gbm_gralloc and mesa.
>>
>> drm_hwc opens the *primary* node in DrmResources::Init() and creates an
>> internal model of what properties/components the device has.
>>
>> gbm_gralloc uses the *render* node during in gbm_dev_create().
>>
>> Mesa uses uses the *render* node during dri_screen creation in
>> dri2_create_screen() and for loading the driver in
>> dri2_initialize_android().
>>
>> However, problematically, drm_hwc uses OpenGL composition as a fallback
>> method, and when doing so mesa has to be able to import buffers, which means
>> mesa has to use a *primary* node.
>>
>> The way this is currently worked around in production systems seems to be to
>> disable drm master authentication. This is at least what ChromeOS & Intel
>> are doing as far as I understand it.
>>
>
> Thanks for kicking this off.
>
> I've done a few tests on 2) with VC4 and 8.1.0_r18. With drm_hwc the primary
> or master on card0 and gbm_gralloc & Mesa each getting their own fd from
> render128, I didn't need any of the DRM authentication hacks in the kernel
> anymore. That's with full overlay composition, everything forced to hwui GL
> composition or everything done through my hacked up ES2 version of glworker
> in drm_hwc (well it made it to launcher until succumbing to a resource leak).
> So I don't think mesa would need a master node and could make do with render.

Thanks for checking this. It seems to match my assumptions, which I
described in my reply to Rob's email.

>
> The one thing that mesa on a render node definitely breaks is flink/GEM names
> which drm_gralloc uses (the Android-x86 version anyway). No flink anything
> with render nodes; drm_gralloc would have to move to dmabuf fds.

I really wonder why those are still in use...

>
> That said, it would finally get rid of the strict coupling between Mesa and
> gralloc. Ripping out the PERFORM and drm_gralloc facsimile in gbm_gralloc
> saves a big bunch of code:
>
> https://github.com/stschake/gbm_gralloc/tree/libdrm_handle_def
>
> With more in mesa/platform_android from the flink stuff.

Nice diffstat. ;)

Best regards,
Tomasz