[Bug 98912] [SKL] ext. HDMI hotplug not working on i7-6700HQ laptop

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=98912

--- Comment #8 from Imre Deak <imre.deak at intel.com> ---
(In reply to raptorteak from comment #7)
> $ sudo i2cdump -y 4 0x40 i
>      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f    0123456789abcdef
> 00: 44 50 2d 48 44 4d 49 20 41 44 41 50 54 4f 52 04    DP-HDMI ADAPTOR?
> 10: a8 00 1c f8 50 53 31 37 35 30 b0 00 00 78 0f 00    ?.??PS1750?..x?.
> 20: 00 00 08 00 00 00 00 00 00 00 00 00 00 00 00 00    ..?.............
> 30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 40: 01 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ??..............
> 50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 60: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00    ................
> 
> Looks like you are right about the adapter. However, drm-tip didn't do the
> trick :< . Unless there is a specific config to enable ?
> 
> Above is a newer dmesg from the drm-tip run.

Thanks, LSPCON is enabled now and the monitor is detected during bootup, but
after replug the adaptor's AUX channel is down for some reason, so detection
will fail. One possibility is that the adaptor switches to LS mode during
unplug and we have to switch back to PCON mode. Could you get the same i2cdump
as above after replugging and try the following patch:

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 9dfbde4..96809cf 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4101,9 +4101,13 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
 static enum drm_connector_status
 intel_dp_detect_dpcd(struct intel_dp *intel_dp)
 {
+       struct intel_lspcon *lspcon = dp_to_lspcon(intel_dp);
        uint8_t *dpcd = intel_dp->dpcd;
        uint8_t type;

+       if (lspcon->active)
+               lspcon_resume(lspcon);
+
        if (!intel_dp_get_dpcd(intel_dp))
                return connector_status_disconnected;

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