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Bug 1494173 - Some text not rendered on Skylake CPUs
Summary: Some text not rendered on Skylake CPUs
Alias: None
Product: Fedora
Classification: Fedora
Component: xorg-x11-drv-intel
Version: 26
Hardware: Unspecified
OS: Unspecified
Target Milestone: ---
Assignee: Adam Jackson
QA Contact: Fedora Extras Quality Assurance
Depends On:
TreeView+ depends on / blocked
Reported: 2017-09-21 15:06 UTC by Jason Tibbitts
Modified: 2018-05-29 12:05 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2018-05-29 12:05:52 UTC
Type: Bug

Attachments (Terms of Use)

Description Jason Tibbitts 2017-09-21 15:06:27 UTC
I have had to disable glamor on my machines due to a separate issue involving display corruption with Matlab.  But unfortunately, when I do this I find that on Skylake machines there are occasional instances where text simply isn't rendered.  This shows up most commonly, of course, in Matlab, but will occasionally show up in other places such as Dolphin (the KDE File manager).  Sadly I can only reliably repeat it in Matlab, where it is immediately obvious as the right-click menu and command window will be missing most of their contents.

I'm disabling glamor using the following in /etc/X11/xorg.conf.d/20-intel-no-glamor.conf:

Section "Device"
        Identifier "Intel Graphics"
        Driver     "intel"
        Option     "AccelMethod" "sna"

I chatted a bit in #intel-gfx and it was suggested that I try "blt".  Interestingly, that also shows the problem.  But if I use "uxa" (which I know is suboptimal on Skylake) the problem goes away.

So some bit of code which is used by both "sna" and "blt" but not by "uxa" is involved here.

Since I can only reliably reproduce this using Matlab, I am willing to obtain a Matlab license for a driver developer.

Comment 1 Jason Tibbitts 2017-09-21 15:16:10 UTC
I should also add that this happens with the stock F26 Intel driver: xorg-x11-drv-intel-2.99.917-28.20160929.fc26 and with the current rawhide version (xorg-x11-drv-intel-2.99.917-30.20160929.fc26).

In #intel-gfx I was pointed at a one-liner patch to sna/kgem.h which I am also running, but it doesn't seem to make much difference:

From 36efca112587e34d06a6ca11aabbebee5c9efaac Mon Sep 17 00:00:00 2001
From: Lyude Paul <thatslyude@gmail.com>
Date: Tue, 22 Aug 2017 12:38:11 -0400
Subject: [PATCH xf86-video-intel] Test fix for bz141238

Signed-off-by: Lyude Paul <thatslyude@gmail.com>
 src/sna/kgem.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/sna/kgem.h b/src/sna/kgem.h
index ded8f78f..ef535faa 100644
--- a/src/sna/kgem.h
+++ b/src/sna/kgem.h
@@ -587,7 +587,7 @@ static inline bool kgem_bo_can_blt(struct kgem *kgem,
                return false;

-       if (kgem->gen >= 0100 && bo->proxy && bo->delta & (1 << 4)) {
+       if (kgem->gen >= 0100 && bo->proxy && bo->delta & 63) {
                DBG(("%s: can not blt to handle=%d, delta=%d\n",
                     __FUNCTION__, bo->handle, bo->delta));
                return false;

Comment 2 Fedora End Of Life 2018-05-03 08:44:04 UTC
This message is a reminder that Fedora 26 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 26. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
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Comment 3 Fedora End Of Life 2018-05-29 12:05:52 UTC
Fedora 26 changed to end-of-life (EOL) status on 2018-05-29. Fedora 26
is no longer maintained, which means that it will not receive any
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