[Bug 109522] drm:intel_dp_start_link_train [i915] *ERROR* failed to enable link training

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=109522

--- Comment #12 from howaboutsynergy at pm.me ---
Can't manually reproduce it, I tried turning monitor off, then back on; tried:
```
sleep 1; xset dpms force suspend; sleep 1; xset dpms force off; sleep 1; xset
dpms force standby
setterm --blank force
```

They all seemed to work so far, so the dmesg output with this patch:
```diff
$ git diff drivers/gpu/drm/i915/intel_dp_link_training.c|tee
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c
b/drivers/gpu/drm/i915/intel_dp_link_training.c
index b59c87daa4f7..e69b2198af89 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -87,6 +87,7 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
        ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_PATTERN_SET,
                                buf, len);

+  DRM_ERROR("ret=%d len=%d\n", ret, len);
        return ret == len;
 }

```

apparently right after the monitor turns on, I get these 5,5,1 each time on
dmesg:
```
$ dmesg --level err
[    3.844322] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[    3.846020] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[    3.848732] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=1 len=1
[   56.871626] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[   56.873573] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[   56.874693] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=1 len=1
[   58.212665] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[   58.214381] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[   58.217124] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=1 len=1
[  103.393851] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[  103.395610] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=5 len=5
[  103.398358] [drm:intel_dp_set_link_train [i915]] *ERROR* ret=1 len=1
```

So this is when it works normally!

When it doesn't work..., I'll have to update in a next comment when I hit it
again. Curious what ret&len I'll get.

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