[Bug 76804] New: font corruption using xf86-video-intel-2.21.15 with sna

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=76804

          Priority: medium
            Bug ID: 76804
          Assignee: chris at chris-wilson.co.uk
           Summary: font corruption using xf86-video-intel-2.21.15 with
                    sna
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
          Severity: normal
    Classification: Unclassified
                OS: Linux (All)
          Reporter: chaujc at gmail.com
          Hardware: x86-64 (AMD64)
            Status: NEW
           Version: unspecified
         Component: Driver/intel
           Product: xorg

Created attachment 96626
  --> https://bugs.freedesktop.org/attachment.cgi?id=96626&action=edit
Image of font corruption in Emacs

After upgrading from xf86-video-intel-2.20.13 to xf86-video-intel-2.21.15 (both
with sna enabled), I see font corruption appear.  This font corruption did not
occur with xf86-video-intel-2.20.13 and does not appear when UXA is used
instead.  

The font corruption occurs across several applications (Firefox, LibreOffice,
Emacs).  The corruption does not occur reliably (i.e, not in the same place
every time), but happens often.  The font corruption disappears when I
highlight the corrupted text (I assume causing it to be redrawn).  


I have found other reports of apparently the same bug at:
https://forums.gentoo.org/viewtopic-t-972582.html (my post),
https://bbs.archlinux.org/viewtopic.php?id=171128, and
http://forum.manjaro.org/index.php?topic=7269.0


Bug 37946 appears similar, but the font corruption appears different; in my
case, the corrupted character does not resemble the actual character.  

Some examples shown in bug 55500 also appear similar, but I do NOT experience
any of the other problems mentioned: flicker, image corruption, and parts of
the screen blanked.  Due to the differences, I believe I am experiencing a
different bug.  


Up until recently, my workaround was to use the older xf86-video-intel-2.20.13,
but a recent ABI change in my upgrade from xorg-server-1.14.3-r2 to
xorg-server-1.15.0 required using the newer xf86-video-intel-2.21.15.  

I am using Gentoo Linux on this computer (if it makes a difference).  I'll be
happy to do what I can to help, but I'm not very familiar with the code & build
environment yet.  Please let me know if I should provide any additional
information or examples to help debug this problem.  


lspci -vnn:
00:02.0 VGA compatible controller [0300]: Intel Corporation Mobile 4 Series
Chipset Integrated Graphics Controller [8086:2a42] (rev 07) (prog-if 00 [VGA
controller])
        Subsystem: Lenovo Device [17aa:20e4]
        Flags: bus master, fast devsel, latency 0, IRQ 42
        Memory at f0000000 (64-bit, non-prefetchable) [size=4M]
        Memory at d0000000 (64-bit, prefetchable) [size=256M]
        I/O ports at 1800 [size=8]
        Expansion ROM at <unassigned> [disabled]
        Capabilities: [90] MSI: Enable+ Count=1/1 Maskable- 64bit-
        Capabilities: [d0] Power Management version 3
        Kernel driver in use: i915

00:02.1 Display controller [0380]: Intel Corporation Mobile 4 Series Chipset
Integrated Graphics Controller [8086:2a43] (rev 07)
        Subsystem: Lenovo Device [17aa:20e4]
        Flags: bus master, fast devsel, latency 0
        Memory at f0400000 (64-bit, non-prefetchable) [size=1M]
        Capabilities: [d0] Power Management version 3

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