[Mesa-dev] [PATCH RFC] egl/dri2: Add dri3 support to x11 platform

Axel Davy axel.davy at ens.fr
Sat Jul 4 01:17:45 PDT 2015

On 04/07/2015 05:18, Boyan Ding wrote :
> Hi Emil,
> On 07/03/2015 10:36 PM, Emil Velikov wrote:
>>> [snip]
>>> +/* FIXME: Is this right? Seems problematic for WL_bind_wayland_display */
>> What seems to be the problem ?
>> Afaik xcb_dri3_open_reply_fds should return an FD which is ok (be that a
>> render_node device, or a master one with explicit auth).
> The problem is that WL_bind_wayland_display don't work under dri3 on
> x11. I only found it yesterday that to get it work, we'll need to add a
> mechanism to pass fd instead of name of dri device in wl_drm protocol.
> Previously, if a wayland client wants to use hardware accelerated EGL,
> it (with the help of libEGL in mesa) will bind to wl_drm object, and
> wl_drm will immediately send the name of dri device to the wayland
> client (actually also libEGL in mesa). After wayland platform code
> opens the device, it has to send the fd to the X server or drm to
> get authentication. Things are different with dri3, where a fd is
> directly sent to the client without the need to authenticate.
> I propose the following addition in wl_drm protocol:
> There are two kinds of wl_drm implementation. One is the current form.
> The other one, called "dri3-capable" (or whatever name), include wl_drm
> object built on dri3 directly or indirectly through wayland platform.
> If a client binds to a "dri3-capable" wl_drm object, it will send a "device"
> event to the client with NULL or empty string (so a client who knows
> nothing about it can safely fail). If the client knows about dri3-capable
> wl_drm object, it will send a request named get_fd and wl_drm will
> respond it with an fd acquired with dri3. If the wl_drm object is not
> "dri3-capable" it will raise an error if it receives a get_fd request,
> so will a "dri3-capable" wl_drm object if it receives authenticate
> request.
> So the following dri3_authenticate function is not needed. Let's not
> expose WL_bind_wayland_display for now, and its enablement
> should be separate patches.

Both XWayland DRI3 and EGL Wayland are able to handle render-nodes, and 
render-nodes have been available for quite some time now. In fact there 
has been several times discussions on wayland irc channel to only 
advertise render-nodes via wl_drm.
Instead of adding a function to wl_drm to get an fd directly, I advocate 
just advertising the render node name (if your device is not a render 
node, it is possible to get the render node name), and then you don't 
have to authenticate.
In case render-nodes are not available, then it's ok not to advertise 
the extension.


Axel Davy

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