[Bug 101167] [BAT][SKL] igt at kms_flip@basic-flip-vs-dpms produces a dmesg-fail

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101167

Jani Nikula <jani.nikula at intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #7 from Jani Nikula <jani.nikula at intel.com> ---
(In reply to Marta Löfstedt from comment #6)
> If I revert:
> 
> "commit 9301397a63b3bf1090dffe846c6f1c8efa032236
> Author: Manasi Navare <manasi.d.navare at intel.com>
> Date:   Thu Apr 6 16:44:19 2017 +0300
> 
>     drm/i915: Implement Link Rate fallback on Link training failure"
> 
> I can't reproduce the test failing. However I still get the dmesg-warn (see
> bug https://bugs.freedesktop.org/show_bug.cgi?id=101144 )

Before the change, we plunge on with channel equalization regardless of
failures during clock recovery phase. By magic, on some machines it'll still
all work despite the errors.

Per spec, the correct thing to do is to check and handle the failures
gracefully, and reducing the link, which Manasi's commit attempts to do.

(In reply to Marta Löfstedt from comment #5)
> But I since the issue hasn't been 100% reproducible I believe we need to
> find a root cause and not just slowing things down.

Agreed. In this case it seems to boil down to DP aux channel communication. On
a whim, please try:

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fc691b8b317c..fb568f75939f 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -2431,6 +2431,8 @@ void intel_dp_sink_dpms(struct intel_dp *intel_dp, int
mode)
 {
        int ret, i;

+       return;
+
        /* Should have a valid DPCD by this point */
        if (intel_dp->dpcd[DP_DPCD_REV] < 0x11)
                return;

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