Re: [PATCH 1/3] drm: Check CRTC compatibility in setplane

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Apr 23, 2014 at 11:26:04AM -0700, Matt Roper wrote:
> On Wed, Apr 23, 2014 at 08:03:50PM +0200, Daniel Vetter wrote:
> > On Wed, Apr 23, 2014 at 10:03:59AM -0700, Matt Roper wrote:
> > > The DRM core setplane code should check that the plane is usable on the
> > > specified CRTC before calling into the driver.
> > > 
> > > Prior to this patch, a plane's possible_crtcs field was purely
> > > informational for userspace and was never actually verified at the
> > > kernel level (aside from the primary plane helper).
> > > 
> > > Cc: dri-devel@lists.freedesktop.org
> > > Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
> > 
> > Do you have a nasty igt somewhere which tries to use a plane on the wrong
> > crtc? Especially useful since our i915 code and hw relies on this.
> > -Daniel
> 
> Not yet; I'll add/modify a test to include that.  I'm still working on
> some other i-g-t test updates for the primary plane stuff based on your
> previous feedback.
> 
> Speaking of i-g-t testing, what is the expected behavior if someone
> issues a pageflip ioctl while the primary plane is disabled?  I'd expect
> it to return an error, but the -EBUSY currently returned by the DRM core
> seems a bit confusing/misleading in my opinion.  The comments indicate
> that the existing assumption is that crtc->primary->fb == NULL indicates 
> a hotplug event that userspace hasn't noticed yet, although now we
> clearly have other ways to hit that error, so I'm not sure EBUSY is
> really the right response.

That comment is outdated since nowadays the kernel doesn't randomly kill a
crtc if its outputs gets unplugged. I think a simple -EINVAL should be
good. We'd need to update kms_flip with that new value though.

A quick grep through the intel ddx shows that we don't really depend on
this either way. -EBUSY for a disabled primary plane (whether the crtc is
on or not doesn't matter imo) really makes no sense.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch