* Issue after drm/i915: prefer wide & slow to fast & narrow in DP configs.
@ 2013-03-20 13:45 Michal Srb
2013-03-20 15:28 ` Jesse Barnes
0 siblings, 1 reply; 2+ messages in thread
From: Michal Srb @ 2013-03-20 13:45 UTC (permalink / raw)
To: intel-gfx
Hi,
I am debugging an issue with IBM POS machine (4852-570, Truman), with
8086:0102 Intel Sandybridge graphic card and internal monitor connected over
display port.
The issue is that sporadically, after mode change, the monitor remains blank.
There is no difference in drm.debug=0xe level log or content of <debugfs>/dri
between the state when monitor displays image and the state when it remains
blank.
(The monitor supports only 1024x768, so every mode change is into this
resolution. It happens when the intel driver switches resolution during boot,
when X starts, X ends, modetest starts or modetest ends.)
I've bisected the cause to this commit:
commit 2514bc510d0c3aadcc5204056bb440fa36845147
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date: Thu Jun 21 15:13:50 2012 -0700
drm/i915: prefer wide & slow to fast & narrow in DP configs
High frequency link configurations have the potential to cause trouble
with long and/or cheap cables, so prefer slow and wide configurations
instead. This patch has the potential to cause trouble for eDP
configurations that lie about available lanes, so if we run into that we
can make it conditional on eDP.
The machine reports to have 2 lanes available and that seems to be correct.
One lane was used before the commit and the screen used to show picture after
every mode change:
[drm:intel_dp_mode_fixup], DP ink computation with max lane count 2 max bw
0a pixel clock 65000KHz
[drm:intel_dp_mode_fixup], DP link bw 0a lane count 1 clock 270000 bpp 24
[drm:intel_dp_mode_fixup], DP link bw required 156000 available 216000
Two lanes are used after the commit and the screen occasionally remains blank
after mode change:
[drm:intel_dp_mode_fixup], DP link computation with max lane count 2 max bw
0a pixel clock 65000KHz
[drm:intel_dp_mode_fixup], DP link bw 06 lane count 2 clock 162000 bpp 24
[drm:intel_dp_mode_fixup], DP link bw required 156000 available 259200
Could you advise me where to look further? Could this be a hardware bug?
Reverting the commit works as a workaround, but doesn't look like correct way
to fix this...
Thank you,
Michal Srb
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Issue after drm/i915: prefer wide & slow to fast & narrow in DP configs.
2013-03-20 13:45 Issue after drm/i915: prefer wide & slow to fast & narrow in DP configs Michal Srb
@ 2013-03-20 15:28 ` Jesse Barnes
0 siblings, 0 replies; 2+ messages in thread
From: Jesse Barnes @ 2013-03-20 15:28 UTC (permalink / raw)
To: Michal Srb; +Cc: intel-gfx
On Wed, 20 Mar 2013 14:45:52 +0100
Michal Srb <msrb@suse.com> wrote:
> Hi,
>
> I am debugging an issue with IBM POS machine (4852-570, Truman), with
> 8086:0102 Intel Sandybridge graphic card and internal monitor connected over
> display port.
>
> The issue is that sporadically, after mode change, the monitor remains blank.
> There is no difference in drm.debug=0xe level log or content of <debugfs>/dri
> between the state when monitor displays image and the state when it remains
> blank.
>
> (The monitor supports only 1024x768, so every mode change is into this
> resolution. It happens when the intel driver switches resolution during boot,
> when X starts, X ends, modetest starts or modetest ends.)
>
> I've bisected the cause to this commit:
>
> commit 2514bc510d0c3aadcc5204056bb440fa36845147
> Author: Jesse Barnes <jbarnes@virtuousgeek.org>
> Date: Thu Jun 21 15:13:50 2012 -0700
>
> drm/i915: prefer wide & slow to fast & narrow in DP configs
>
> High frequency link configurations have the potential to cause trouble
> with long and/or cheap cables, so prefer slow and wide configurations
> instead. This patch has the potential to cause trouble for eDP
> configurations that lie about available lanes, so if we run into that we
> can make it conditional on eDP.
>
>
> The machine reports to have 2 lanes available and that seems to be correct.
> One lane was used before the commit and the screen used to show picture after
> every mode change:
>
> [drm:intel_dp_mode_fixup], DP ink computation with max lane count 2 max bw
> 0a pixel clock 65000KHz
> [drm:intel_dp_mode_fixup], DP link bw 0a lane count 1 clock 270000 bpp 24
> [drm:intel_dp_mode_fixup], DP link bw required 156000 available 216000
>
> Two lanes are used after the commit and the screen occasionally remains blank
> after mode change:
>
> [drm:intel_dp_mode_fixup], DP link computation with max lane count 2 max bw
> 0a pixel clock 65000KHz
> [drm:intel_dp_mode_fixup], DP link bw 06 lane count 2 clock 162000 bpp 24
> [drm:intel_dp_mode_fixup], DP link bw required 156000 available 259200
>
>
> Could you advise me where to look further? Could this be a hardware bug?
> Reverting the commit works as a workaround, but doesn't look like correct way
> to fix this...
There's nothing else in the log about aux failures? Just that the
training apparently succeeded but you ended up with a blank screen?
--
Jesse Barnes, Intel Open Source Technology Center
^ permalink raw reply [flat|nested] 2+ messages in thread
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2013-03-20 13:45 Issue after drm/i915: prefer wide & slow to fast & narrow in DP configs Michal Srb
2013-03-20 15:28 ` Jesse Barnes
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