Bug 103400

I think the problem is that your display has incorrect eDP DPCD information (bit 3 of DPCD register 0x006 is not set, instead the whole register is set to 0x03). Please try this debug patch to see if it helps:

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index aa75f55eeb61..b2bb7d2941f3 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3736,8 +3736,7 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 	}
 
 	/* Read the eDP Display control capabilities registers */
-	if ((intel_dp->dpcd[DP_EDP_CONFIGURATION_CAP] & DP_DPCD_DISPLAY_CONTROL_CAPABLE) &&
-	    drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
+	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_DPCD_REV,
 			     intel_dp->edp_dpcd, sizeof(intel_dp->edp_dpcd)) ==
 			     sizeof(intel_dp->edp_dpcd))
 		DRM_DEBUG_KMS("EDP DPCD : %*ph\n", (int) sizeof(intel_dp->edp_dpcd),

Please let us know the contents of that "EDP DPCD" debug message with this change.

Hello,

Thanks for your reply.
The patch indeed helps : with it, my virtual console now shows up
successfully without nomodeset.
Here's the content of EDP DPCD with the debug patch:
> $ dmesg | grep "EDP DPCD"
> [   19.924664] [drm:intel_dp_init_connector [i915]] EDP DPCD : 12 00 00

Best regards,

(In reply to Nicolas P. from comment #2)
> The patch indeed helps : with it, my virtual console now shows up
> successfully without nomodeset.

Thanks for testing.

> Here's the content of EDP DPCD with the debug patch:
> > $ dmesg | grep "EDP DPCD"
> > [   19.924664] [drm:intel_dp_init_connector [i915]] EDP DPCD : 12 00 00

Auch, that's garbage too, in violation of the eDP spec. :(

I'll try to cook up something.

Effectively same patch as comment #1, with polish:

http://patchwork.freedesktop.org/patch/msgid/20171026142932.17737-1-jani.nikula@intel.com

Can you please attach the entire DPCD here for posterity? Oh and EDID would be nice as well.

This should normally work (needs CONFIG_DRM_DP_AUX_CHARDEV=y in the kernel config):
cat /dev/drm_dp_aux0 > dpcd
But if there are read errors you will have to use someting like ddrescue to read it out.

For the EDID you can use:
cat /sys/class/drm/card0-eDP-1/edid > edid

Hello,

Jani Nikula 2017-10-26 14:36:25 UTC:
> Effectively same patch as comment #1, with polish:

Thanks a lot. :)

Ville Syrjala 2017-10-26 14:49:59 UTC:
> Can you please attach the entire DPCD here for posterity? Oh and EDID would be nice as well.

Sure, I will attach them right away.

Best regards,

Created attachment 135089 [details]
edid

Created attachment 135090 [details]
dpcd

Fixed by

commit 0501a3b0eb01ac2209ef6fce76153e5d6b07034e
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Thu Oct 26 17:29:31 2017 +0300

    drm/i915/edp: read edp display control registers unconditionally

and cc: stable to backport it to stable kernels.

Thanks for the report and testing.