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<b><a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [snb DP-to-DVI dongle] miniDP to external monitor with DVI-D via miniDP to DVI-D adapter and blank screen"
href="https://bugs.freedesktop.org/show_bug.cgi?id=106596#c11">Comment # 11</a>
on <a class="bz_bug_link
bz_status_NEEDINFO "
title="NEEDINFO - [snb DP-to-DVI dongle] miniDP to external monitor with DVI-D via miniDP to DVI-D adapter and blank screen"
href="https://bugs.freedesktop.org/show_bug.cgi?id=106596">bug 106596</a>
from <span class="vcard"><a class="email" href="mailto:ville.syrjala@linux.intel.com" title="Ville Syrjala <ville.syrjala@linux.intel.com>"> <span class="fn">Ville Syrjala</span></a>
</span></b>
<pre>(In reply to Jani Nikula from <a href="show_bug.cgi?id=106596#c9">comment #9</a>)
<span class="quote">> (In reply to genpur from <a href="show_bug.cgi?id=106596#c7">comment #7</a>)
> > When adapter is disconnected :
> > LC_MESSAGES=en_UK.UTF-8 sudo dd if=/dev/drm_dp_aux0 bs=1 skip=$((0x200))
> > count=1 | od -tx1
> > dd: error reading '/dev/drm_dp_aux0': Connection timed out
>
> As expected.
>
> > When adapter is connected :
> > LC_MESSAGES=en_UK.UTF-8 sudo dd if=/dev/drm_dp_aux0 bs=1 skip=$((0x200))
> > count=1 | od -tx1
> > 1+0 records in
> > 1+0 records out
> > 1 byte copied, 0.000779381 s, 1.3 kB/s
> > 0000000 00
>
> That 00 tells us the adapter thinks there are no displays connected to it.
> That should dynamically change depending on the display being
> plugged/unplugged into the other end of the cable, and generate a hotplug
> event. Please double check with a display, and ensure it's on.
>
> How about
>
> dd if=/dev/drm_dp_aux0 bs=1 skip=$((0x80)) count=16 | od -tx1
>
> Ville, perhaps we should only trust sink count if downstream port is hotplug
> capable, and assume 1 otherwise? Regardless of what the spec says. See the
> sink count handling in intel_dp_detect_dpcd() - we never reach that if sink
> count is 0 in intel_dp_get_dpcd(). Not very consistent.</span >
IIRC I was arguing about SINK_COUNT vs. hpd capable years ago with someone.
Can't really remember what the issue was though.
Reporter, please attach the full dpcd dump from 'dd if=/dev/drm_dp_aux0' to the
bug (should be 1MiB in size, if it comes out short use ddrescue instead). Do
make sure the display is powered on and connected to the dongle when you do
this.</pre>
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