[Intel-gfx] [drm:drm_calc_timestamping_constants [drm]] *ERROR* crtc 21: Can't calculate constants, dotclock = 0!

Ville Syrjälä ville.syrjala at linux.intel.com
Thu Oct 1 04:13:09 PDT 2015

On Thu, Oct 01, 2015 at 11:41:34AM +0200, Jiri Kosina wrote:
> Hi,
> since I've updated on my thinkpad x200s to latest Linus' tree (3235031), I 
> am getting a lot of
> 	[drm:drm_calc_timestamping_constants [drm]] *ERROR* crtc 21: Can't calculate constants, dotclock = 0!

What's a lot? I think you should see at most a few during driver load,
and maybe resume.

If you're seeing more during runtime, then I think there must be a more
serious bug somewhere.

> googling revealed this patch:
> 	http://permalink.gmane.org/gmane.comp.freedesktop.xorg.drivers.intel/67471
> is there any reason why it's not present upstream?

There's a v2 of that patch in some tree. Hmm. Seems to be in
drm-intel-next-queued. Maybe it should get bumped to -fixes?

There's also another one that kills some of those message on certain
0f64614dde17 drm/i915: Fix clock readout when pipes are enabled w/o ports

Ville Syrjälä
Intel OTC

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