Bug 101439

Summary:	[IGT] kms_flip@basic-flip-vs-wf_blank vblank interval differs from modeline
Product:	DRI	Reporter:	Tomi Sarvela <tomi.p.sarvela>
Component:	DRM/Intel	Assignee:	Intel GFX Bugs mailing list <intel-gfx-bugs>
Status:	CLOSED FIXED	QA Contact:	Intel GFX Bugs mailing list <intel-gfx-bugs>
Severity:	normal
Priority:	medium	CC:	bugs, intel-gfx-bugs
Version:	DRI git
Hardware:	x86-64 (AMD64)
OS:	Linux (All)
Whiteboard:	ReadyForDev
i915 platform:	BYT, G45, GM45, HSW, I965G, I965GM, ILK, IVB, SNB	i915 features:	display/Other

Description Tomi Sarvela 2017-06-15 07:06:27 UTC

Piglit was changed to consider stderr output as WARN, and this exposed problem with kms_flip@basic-flip-vs-wf_blank test on older gens (Gens 4 to 7)

Affected testhosts: Broadwater, Eagle Lake, Cantiga, Iron Lake, Sandy Bridge, Ivy Lake, Haswell-R (curiously, not Haswell K-CPUs)

Errors are in form:

(kms_flip:2174) WARNING: vblank interval differs from modeline! expected 16665.6us, measured 16717us +- 0.000us, difference 51.4us (inf sigma)
(kms_flip:2174) WARNING: vblank interval differs from modeline! expected 16665.6us, measured 16717us +- 0.250us, difference 51.5us (205.9 sigma)
(kms_flip:2174) WARNING: vblank interval differs from modeline! expected 16666.7us, measured 16633us +- 0.250us, difference 33.6us (134.4 sigma)
(kms_flip:2174) WARNING: vblank interval differs from modeline! expected 16666.7us, measured 16633us +- 0.250us, difference 33.6us (134.4 sigma)

Comment 1 Maarten Lankhorst 2017-06-15 13:31:22 UTC

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.

Is kms_setmode.basic consistently failing with the same error too btw?

Comment 2 Martin Peres 2017-06-15 13:55:09 UTC

(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.

Good to know.

> 
> Is kms_setmode.basic consistently failing with the same error too btw?

Well, whenever it fails, it has this warning. So, I guess it must always be there!

Comment 3 Ville Syrjala 2017-06-16 17:15:39 UTC

(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.

Comment 4 Martin Peres 2017-06-20 13:04:30 UTC

Fixed in IGT (https://cgit.freedesktop.org/xorg/app/intel-gpu-tools/commit/?id=1345a21886d7606b59225d3c4f5e03fa913e1ac7).

Comment 5 Maarten Lankhorst 2017-06-21 08:22:25 UTC

Yeah, but note it's still broken in kms_setmode.basic, but I guess it's good enough for this specific bug. :)

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