[Mesa-dev] [PATCH] egl: Don't add hardware device if there is no render node v2.

[Emil Velikov]

On Mon, 17 Jun 2019 at 19:16, Ilia Mirkin <imirkin at alum.mit.edu> wrote:
>
> On Mon, Jun 17, 2019 at 6:37 AM <Mathias.Froehlich at gmx.net> wrote:
> >
> > From: Mathias Fröhlich <Mathias.Froehlich at gmx.net>
> >
> >
> > Emil,
> >
> > that one probably matches your original intent then.
> >
> > please review
> > Thanks
> >
> > Mathias
> >
> >
> > Do not offer a hardware drm backed egl device if no render node
> > is available. The current implementation will fail on this
> > egl device. On top it issues a warning that is actually missleading.
> > There are finally more error paths that can fail on the way to a
> > hardware backed egl device. Fixing all of them would kind of require
> > opening the drm device and see if there is a usable driver associated
> > with the device. The taken approach avoids a full probe and fixes at
> > least this kind of problem on kvm virtualization hosts I observe here.
> >
> > Signed-off-by: Mathias Fröhlich <Mathias.Froehlich at web.de>
> > ---
> >  src/egl/main/egldevice.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/src/egl/main/egldevice.c b/src/egl/main/egldevice.c
> > index 76b8960fa5b..99d8a6c1886 100644
> > --- a/src/egl/main/egldevice.c
> > +++ b/src/egl/main/egldevice.c
> > @@ -108,9 +108,9 @@ static int
> >  _eglAddDRMDevice(drmDevicePtr device, _EGLDevice **out_dev)
> >  {
> >     _EGLDevice *dev;
> > +   const int wanted_nodes = 1 << DRM_NODE_RENDER | 1 << DRM_NODE_PRIMARY;
>
> Why check for primary? Why require both at this point? I guess the
> original intent was to require render *or* primary... but some devices
> will not have a primary node if they don't have any outputs...
>
My original intent was to require both, although I got it wrong.

Why we require both - simple the spec more or less mandates a card/primary node.
Since there an be other software running hence getting authenticated
will be a pita and primary nodes are not accessible* render node seems
like the only robust solution.

HTH
Emil
* There's a bit more to it:
Users not in the video group and w/o systemd - opening the primary
node will fail with EPERM.
Platforms running systemd - logind relaxes the primary node
permission, only when a local user has logged in.