[Intel-gfx] Possible 4.5 i915 Skylake regression

Sat Mar 12 02:16:22 UTC 2016

On Mon, Feb 22, 2016 at 7:13 PM, Andy Lutomirski <luto at amacapital.net> wrote:
> On Wed, Feb 17, 2016 at 5:36 PM, Andy Lutomirski <luto at amacapital.net> wrote:
>> On Wed, Feb 17, 2016 at 8:18 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>> On Tue, Feb 16, 2016 at 09:26:35AM -0800, Andy Lutomirski wrote:
>>>> On Tue, Feb 16, 2016 at 9:12 AM, Andy Lutomirski <luto at amacapital.net> wrote:
>>>> > On Tue, Feb 16, 2016 at 8:12 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
>>>> >> On Mon, Feb 15, 2016 at 06:58:33AM -0800, Andy Lutomirski wrote:
>>>> >>> On Sun, Feb 14, 2016 at 6:59 PM, Andy Lutomirski <luto at kernel.org> wrote:
>>>> >>> > Hi-
>>>> >>> >
>>>> >>> > On 4.5-rc3 on a Dell XPS 13 9350 (Skylake i915, no nvidia on this
>>>> >>> > model), shortly after resume, I saw a single black flash on the
>>>> >>> > screen.  The log said:
>>>> >>> >
>>>> >>> > [Feb13 07:05] [drm:intel_cpu_fifo_underrun_irq_handler [i915]] *ERROR*
>>>> >>> > CPU pipe A FIFO underrun
>>>> >>> >
>>>> >>> > I haven't seen this on 4.4.
>>>> >>> >
>>>> >>> > I'd be happy to dig up debugging info, but I don't know what would be
>>>> >>> > useful.  I have no i915 module options set.
>>>> >>>
>>>> >>> It's flashing quite frequently now, although I seem to get the
>>>> >>> underrun warning only once per resume.
>>>> >>
>>>> >> We shut up the warning irq source to avoid hijacking an entire cpu core
>>>> >> ;-)
>>>> >>
>>>> >> There's a fix from Matt right after 4.5-rc4 in Linus' branch. I'm hoping
>>>> >> that should help.
>>>> >
>>>> > Do you mean:
>>>> >
>>>> > commit e2e407dc093f530b771ee8bf8fe1be41e3cea8b3
>>>> > Author: Matt Roper <matthew.d.roper at intel.com>
>>>> > Date:   Mon Feb 8 11:05:28 2016 -0800
>>>> >
>>>> >     drm/i915: Pretend cursor is always on for ILK-style WM calculations (v2)
>>>> >
>>>> > If so, it didn't help.  I'm currently doing a full rebuild just in
>>>> > case I messed something up, though.
>>>> >
>>>>
>>>> Definitely not fixed.  It seems to be okay after a reboot until the
>>>> first suspend/resume.
>>>>
>>>> This happened after resuming.  Five cents says it's the root cause.
>>>
>>> That's interesting, but doesn't ring a bell unfortunately. Can you try to
>>> attempt a bisect?
>>
>> I probably can, but it's very slow.  Is there a reasonably
>> straightforward way to instrument the watermark computation to see
>> what's going wrong?  I'm reasonably confident that the bug is in the
>> resume code or in something that only happens on resume, since I still
>> haven't seen underruns after rebooting before suspending.
>>
>
> With some instrumentation applied, I got this:
>
> [  369.471064] skl_update_wm(crtc-0): computed update
> [  369.471072] skl_update_other_pipe_wm(crtc-0): no change
> [  369.471075] skl_write_wm_values...
> [  369.471078]  CRTC crtc-0 pipe A
> [  369.471083]   wm_linetime = 121
> [  369.471086]   plane_wm level 0 plane 0 = 2147500036
> [  369.471090]   plane_wm level 0 plane 1 = 0
> [  369.471094]   plane_wm level 0 cursor = 2147500036
> [  369.471097]   plane_wm level 1 plane 0 = 2147516439
> [  369.471101]   plane_wm level 1 plane 1 = 0
> [  369.471104]   plane_wm level 1 cursor = 2147516439
> [  369.471108]   plane_wm level 2 plane 0 = 2147516448
> [  369.471111]   plane_wm level 2 plane 1 = 0
> [  369.471115]   plane_wm level 2 cursor = 0
> [  369.471118]   plane_wm level 3 plane 0 = 2147532837
> [  369.471121]   plane_wm level 3 plane 1 = 0
> [  369.471125]   plane_wm level 3 cursor = 0
> [  369.471128]   plane_wm level 4 plane 0 = 2147565639
> [  369.471131]   plane_wm level 4 plane 1 = 0
> [  369.471135]   plane_wm level 4 cursor = 0
> [  369.471138]   plane_wm level 5 plane 0 = 2147582038
> [  369.471141]   plane_wm level 5 plane 1 = 0
> [  369.471145]   plane_wm level 5 cursor = 0
> [  369.471148]   plane_wm level 6 plane 0 = 2147582044
> [  369.471151]   plane_wm level 6 plane 1 = 0
> [  369.471155]   plane_wm level 6 cursor = 0
> [  369.471158]   plane_wm level 7 plane 0 = 2147598443
> [  369.471161]   plane_wm level 7 plane 1 = 0
> [  369.471164]   plane_wm level 7 cursor = 0
> [  369.471168]   wm_trans plane 0 = 0
> [  369.471171]   wm_trans plane 1 = 0
> [  369.471174]   wm_trans cursor = 0
> [  369.471182]  CRTC crtc-1 pipe B
> [  369.471184]   clean
> [  369.471186]  CRTC crtc-2 pipe C
> [  369.471189]   clean
> [  369.471226] skl_update_wm(crtc-0): no update
> [  372.068755] [drm:intel_cpu_fifo_underrun_irq_handler [i915]]
> *ERROR* CPU pipe A FIFO underrun
> [  373.399396] skl_update_wm(crtc-0): computed update
> [  373.399408] skl_update_other_pipe_wm(crtc-0): no change
> [  373.399413] skl_write_wm_values...
> [  373.399418]  CRTC crtc-0 pipe A
> [  373.399426]   wm_linetime = 121
> [  373.399431]   plane_wm level 0 plane 0 = 2147500036
> [  373.399438]   plane_wm level 0 plane 1 = 0
> [  373.399443]   plane_wm level 0 cursor = 16388
> [  373.399449]   plane_wm level 1 plane 0 = 2147516439
> [  373.399455]   plane_wm level 1 plane 1 = 0
> [  373.399460]   plane_wm level 1 cursor = 32791
> [  373.399465]   plane_wm level 2 plane 0 = 2147516448
> [  373.399471]   plane_wm level 2 plane 1 = 0
> [  373.399476]   plane_wm level 2 cursor = 0
> [  373.399481]   plane_wm level 3 plane 0 = 2147532837
> [  373.399486]   plane_wm level 3 plane 1 = 0
> [  373.399491]   plane_wm level 3 cursor = 0
> [  373.399497]   plane_wm level 4 plane 0 = 2147565639
> [  373.399502]   plane_wm level 4 plane 1 = 0
> [  373.399557]   plane_wm level 4 cursor = 0
> [  373.399562]   plane_wm level 5 plane 0 = 2147582038
> [  373.399568]   plane_wm level 5 plane 1 = 0
> [  373.399573]   plane_wm level 5 cursor = 0
> [  373.399578]   plane_wm level 6 plane 0 = 2147582044
> [  373.399591]   plane_wm level 6 plane 1 = 0
> [  373.399596]   plane_wm level 6 cursor = 0
> [  373.399602]   plane_wm level 7 plane 0 = 2147598443
> [  373.399607]   plane_wm level 7 plane 1 = 0
> [  373.399612]   plane_wm level 7 cursor = 0
> [  373.399617]   wm_trans plane 0 = 0
> [  373.399623]   wm_trans plane 1 = 0
> [  373.399627]   wm_trans cursor = 0
> [  373.399638]  CRTC crtc-1 pipe B
> [  373.399642]   clean
> [  373.399646]  CRTC crtc-2 pipe C
> [  373.399650]   clean
>
> The diff between those two dumps was:
>
> --- a.txt    2016-02-22 18:56:32.613058614 -0800
> +++ b.txt    2016-02-22 18:56:49.219079057 -0800
> @@ -3,10 +3,10 @@
>    wm_linetime = 121
>    plane_wm level 0 plane 0 = 2147500036
>    plane_wm level 0 plane 1 = 0
> -  plane_wm level 0 cursor = 2147500036
> +  plane_wm level 0 cursor = 16388
>    plane_wm level 1 plane 0 = 2147516439
>    plane_wm level 1 plane 1 = 0
> -  plane_wm level 1 cursor = 2147516439
> +  plane_wm level 1 cursor = 32791
>    plane_wm level 2 plane 0 = 2147516448
>    plane_wm level 2 plane 1 = 0
>    plane_wm level 2 cursor = 0
>
>
> The code that generated this is attached.
>
> Is the fix from Matt that you mentioned this one:
>
> commit e2e407dc093f530b771ee8bf8fe1be41e3cea8b3
> Author: Matt Roper <matthew.d.roper at intel.com>
> Date:   Mon Feb 8 11:05:28 2016 -0800
>
>     drm/i915: Pretend cursor is always on for ILK-style WM calculations (v2)
>
> On brief inspection, it doesn't look like that patch will have any
> effect on Skylake.
>

Re-ping.

This is still broken AFAICT, and it's also not fixed in drm-intel-nightly.