[Intel-gfx] [PATCH 1/6] drm: Let userspace check if driver supports modeset

[Chris Wilson]

Quoting Souza, Jose (2018-07-17 18:02:17)
> On Tue, 2018-07-17 at 08:28 +0100, Chris Wilson wrote:
> > Quoting José Roberto de Souza (2018-07-16 23:38:36)
> > > GPU accelerators usually don't have display block or the display
> > > driver part can be disable when building driver(for servers it save
> > > some resources) so it is important let userspace check this
> > > capability too.
> > 
> > We currently communicate that by having no modeset resources. What
> > does
> > another cap bit accomplish that we don't already know?
> 
> This is a hackish way to check if driver support modeset,
> drmModeGetResources()/drm_mode_getresources() can fail and return null
> by other reasons and just check for the errno value can be misleading
> too.

Do not confuse libdrm with the ioctl. You do not need to allocate
anything for such a check, and it is being used directly without
allocations as a has-kms check.

More to the point existing userspace determines modeset capability
through the reported resources. Your changelog needs to explain why they
are inadequate and how you plan to coordinate your fix with userspace.
As it stands you are introducing uABI with no user...
-Chris