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List:       freedesktop-xorg-devel
Subject:    Re: [PATCH xserver 1/3] xwayland: Add hook to check wl interface for glamor
From:       Olivier Fourdan <ofourdan () redhat ! com>
Date:       2018-05-31 9:12:52
Message-ID: CAP=2yyQDwhyX0MH+cpjr-vOM5Ftct740pTo5Py51OiLe8UF2jw () mail ! gmail ! com
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Hi Lyude,

On Wed, May 30, 2018 at 9:31 PM, Lyude Paul <lyude@redhat.com> wrote:
> NAK. I'm starting to see the problems with this approach I originally hit now.
>
> So: there's some unexpected catches when it comes to EGL client extensions. On
> a system using glvnd with the nvidia driver, the EGL client extension list
> will have /both/ the client extensions for the nvidia EGL driver and the
> client extensions for the Mesa driver. An example from my test machine:
>
> EGL client extensions string:
>     EGL_EXT_platform_base EGL_EXT_device_base # ← nvidia!
>     EGL_KHR_client_get_all_proc_addresses EGL_EXT_client_extensions
>     EGL_KHR_debug EGL_EXT_platform_x11 EGL_EXT_platform_device
>     EGL_EXT_platform_wayland EGL_MESA_platform_gbm # ← mesa!
>     EGL_MESA_platform_surfaceless
>
> This is fine, but what it means is that we're going to have to take the
> presence of either of these extensions as a sign that their respective EGL
> backends -might- be there. e.g. we can't try to make a choice on avoiding
> trying EGLStreams simply because GBM might be there, which is currently what
> this patch does:
>
>  * During init, xwl_glamor_should_use_gbm() tells us we should prefer GBM over
>    EGLStreams
>  * We select the gbm egl backend's hook for checking for the wl interfaces
>  * In xwl_screen_init(), we check for wl_drm and don't see it
>  * xwl_glamor_has_wl_interface() returns FALSE, which makes us disable glamor
>    and fall back to software rendering

I see...

Problem is that we need to check for the interfaces and can do so only
once we're connected to the Wayland display, after we called
xwl_glamor_init_gbm() or xwl_glamor_init_eglstream() which setup the
init_wl_registry() handler to read the wl_registry advertised by the
compositor, and this is part of either xwl_gbm_private or
xwl_eglstream_private structures which get allocated once we've
selected the backend... So this is a chicken and egg situation here.

So those interfaces for all backends, wl_drm, wl_eglstream_display,
wl_eglstream_controller, and init_wl_registry() need to be moved out
of the egl_backend, so that we can read *all* the available Wayland
interfaces first and then decide which backend to use based on *both*
EGL extensions available *and* Wayland interfaces as well.

That's a bit of refactoring of the egl_backend code, working on it...

[...]

Cheers,
Olivier
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