[Intel-gfx] [PATCH 05/10] drm/i915: Use drm_vblank_count() on gen2 for crc frame count

Daniel Vetter daniel at ffwll.ch
Wed Dec 16 07:28:36 PST 2015

On Wed, Dec 16, 2015 at 02:51:20PM +0200, Ville Syrjälä wrote:
> On Wed, Dec 16, 2015 at 11:30:19AM +0100, Daniel Vetter wrote:
> > On Mon, Dec 14, 2015 at 06:23:44PM +0200, ville.syrjala at linux.intel.com wrote:
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > Gen2 doesn't have a hardware frame counter, so let's use the sw
> > > counter value instead.
> > > 
> > > Testcase: igt/kms_pipe_crc_basic/read-crc-pipe-?-frame-sequence
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > 
> > I think the better test is skip the testcase if all frame numbers are 0.
> > Not sure it's worth it to hack this up.
> What's the problem with it? A few extra lines of code?

Well the idea of sampling the hw irq counter is that we'd notice when we
start missing something. Sampling the baked vblank counter isn't really
useful in that regard I think.

Otoh we could just sample the official vblank counter, and then a test
could schedule a flip for a given frame and check that the crc changes at
the right frame (using continuous sampling). That would indeed be useful.
This here just looks like a few random changes to appease a fairly
arbitrary testcase.
Daniel Vetter
Software Engineer, Intel Corporation

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