[Bug 108687] ThinkPad T450 - Broadwell-U: [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=108687

--- Comment #9 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Diego Viola from comment #8)
> Created attachment 142414 [details]
> dmesg w/ drm.debug=0xe exhibiting the error (no xrandr)
> 
> I've ran another dmesg capture with drm.debug=0xe and got another error:
> 
> [22701.493597] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to get
> link status
> [22701.493635] [drm:intel_dp_start_link_train [i915]] [CONNECTOR:72:DP-1]
> Link Training failed at link rate = 162000, lane count = 4
> 
> I didn't change modes with xrandr at all this time, nor turned off the
> monitor manually.
> 
> I've had the screen turn off by default (power saving) a few times though.

Is that done by the xserver dpms?

First we turn off the crtcs (dpms off perhaps?):
[19310.376450] [drm:intel_disable_pipe [i915]] disabling pipe A
[19310.434354] [drm:intel_disable_pipe [i915]] disabling pipe B

A while later the external display disappears:
[22700.475730] [drm:i915_hotplug_work_func [i915]] Connector DP-1 (pin 5)
received hotplug event.
[22700.475804] [drm:intel_dp_detect [i915]] [CONNECTOR:72:DP-1]
[22700.475883] [drm:intel_encoder_hotplug [i915]] [CONNECTOR:72:DP-1] status
updated from connected to disconnected

Then we try to turn on the crtcs (dpms on?):
[22701.493597] [drm:intel_dp_start_link_train [i915]] *ERROR* failed to get
link status
[22701.493635] [drm:intel_dp_start_link_train [i915]] [CONNECTOR:72:DP-1] Link
Training failed at link rate = 162000, lane count = 4
[22701.493697] [drm:intel_dp_modeset_retry_work_fn [i915]] [CONNECTOR:72:DP-1]
[22701.494234] [drm:intel_enable_pipe [i915]] enabling pipe B

And later the external
[22702.090350] [drm:ibx_hpd_irq_handler [i915]] hotplug event received, stat
0x00200000, dig 0x10101012, pins 0x00000020
[22702.090423] [drm:intel_hpd_irq_handler [i915]] digital hpd port B - long
[22702.090494] [drm:intel_hpd_irq_handler [i915]] Received HPD interrupt on PIN
5 - cnt: 0
[22702.090583] [drm:intel_dp_hpd_pulse [i915]] got hpd irq on port B - long
[22702.090661] [drm:i915_hotplug_work_func [i915]] running encoder hotplug
functions
[22702.090732] [drm:i915_hotplug_work_func [i915]] Connector DP-1 (pin 5)
received hotplug event.

And we then succesfully retrain the link:
[22702.105236] [drm:intel_dp_start_link_train [i915]] [CONNECTOR:72:DP-1] Link
Training Passed at Link Rate = 162000, Lane count = 4

So looks pretty much as expected I suppose. The only slight mystery is who
tried to enable the crtc when the display wasn't around. But I suppose that
could just be the xserver dpms thing.

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