[Bug 101439] [IGT] kms_flip at basic-flip-vs-wf_blank vblank interval differs from modeline

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101439

--- Comment #3 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Maarten Lankhorst from comment #1)
> I've seen this error in bug 100215 too. It appears to be that with 36 bpp
> the fake dongle gets a clock speed slightly different from the expected
> vblank interval, so this is a real bug.

I wouldn't go as far as claiming this is a bug. The difference (at least in the
snippets in comment #1) is .2%-.3%, which well within the .5% limit that VESA
has specified in some standard.

There is a real bug in the driver in that it doesn't actually check if the
clock we got is close enough or not. But if we had such a check (and it used
the .5% as its guideline) then it wouldn't have tripped in this case. The state
readout does do a check like that but I think it allows the error to be quite
big.

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