[PATCH xserver v3] autobind GPUs to the screen

Eric Anholt eric at anholt.net
Fri Mar 17 20:58:10 UTC 2017

Hans de Goede <hdegoede at redhat.com> writes:

> From: Dave Airlie <airlied at redhat.com>
> This is a modified version of a patch we've been carry-ing in Fedora and


> RHEL for years now. This patch automatically adds secondary GPUs to the
> master as output sink / offload source making e.g. the use of
> slave-outputs just work, with requiring the user to manually run
> "xrandr --setprovideroutputsource" before he can hookup an external
> monitor to his hybrid graphics laptop.
> There is one problem with this patch, which is why it was not upstreamed
> before. What to do when a secondary GPU gets detected really is a policy
> decission (e.g. one may want to autobind PCI GPUs but not USB ones) and
> as such should be under control of the Desktop Environment.
> Unconditionally adding autobinding support to the xserver will result
> in races between the DE dealing with the hotplug of a secondary GPU
> and the server itself dealing with it.

Will there actually be races?  In the current patch, at least, doesn't
the new GPU get autoconfigured before the randr change notification goes

> However we've waited for years for any Desktop Environments to actually
> start doing some sort of autoconfiguration of secondary GPUs and there
> is still not a single DE dealing with this, so I believe that it is
> time to upstream this now.
> To avoid potential future problems if any DEs get support for doing
> secondary GPU configuration themselves, the new autobind functionality
> is made optional. Since no DEs currently support doing this themselves it
> is enabled by default. When DEs grow support for doing this themselves
> they can disable the servers autobinding through the servers cmdline or a
> xorg.conf snippet.

I think this is a sensible default.  It also helped with getting X up on
my VC4 + CLCD platform.

Reviewed-by: Eric Anholt <eric at anholt.net>
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