port-amd64/55023: pixelation under X

[rcbixler%nyx.net@localhost]

>Number:         55023
>Category:       port-amd64
>Synopsis:       pixelation under X
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-amd64-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Wed Feb 26 15:50:00 +0000 2020
>Originator:     Roy Bixler
>Release:        NetBSD 9
>Organization:
>Environment:
NetBSD localhost 9.0_STABLE NetBSD 9.0_STABLE (GENERIC) #0: Tue Feb 25 18:40:44 UTC 2020  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64
>Description:
Using a browser under X, I sometimes see pixelation or distortion when scrolling.  I sometimes also see this when entering text into the URL bar.  If I wait long enough, it goes away.  I first saw this problem under NetBSD-9 and still see it under the current stable version.  The problem did not occur under NetBSD-8 or 8.1.  The hardware is a Lenovo Thinkpad X1 Carbon.

When booting, I see a couple of errors:

[     8.683492] kern info: [drm] Memory usable by graphics device = 2048M
[     8.683492] kern info: [drm] Supports vblank timestamp caching Rev 2 (21.10.2013).
[     8.683492] kern info: [drm] Driver supports precise vblank timestamp query.
[     8.683492] kern info: [drm] failed to find VBIOS tables
[     8.683492] i915drmkms0: interrupting at ioapic0 pin 16 (i915drmkms0)
[     8.783570] kern info: [drm] GMBUS [i915 gmbus vga] timed out, falling back to bit banging on pin 2
[     8.903664] kern info: [drm] GMBUS [i915 gmbus dpb] timed out, falling back to bit banging on pin 5
[     8.963710] intelfb0 at i915drmkms0
[     8.963710] intelfb0: framebuffer at 0xffffc48063d2a000, size 1600x900, depth 32, stride 6400
[     9.223915] kern error: [drm:(/usr/src/sys/external/bsd/drm2/dist/drm/i915/intel_fifo_underrun.c:230)cpt_set_fifo_underrun_reporting] *ERROR* uncleared pch fifo underrun on pch transcoder A
[     9.223915] kern error: [drm:(/usr/src/sys/external/bsd/drm2/dist/drm/i915/intel_fifo_underrun.c:381)intel_pch_fifo_underrun_irq_handler] *ERROR* PCH transcoder A FIFO underrun

>How-To-Repeat:
Start X, then start up a browser such as "netsurf".  Observe pixelation either in the URL bar or when scrolling down.  The problem happens often, but not always.

>Fix:
Revert to NetBSD-8 or 8.1