<html>
<head>
<base href="https://bugs.freedesktop.org/">
</head>
<body>
<p>
<div>
<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - No internal display on kernels > 4.4.x"
href="https://bugs.freedesktop.org/show_bug.cgi?id=105406#c26">Comment # 26</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - No internal display on kernels > 4.4.x"
href="https://bugs.freedesktop.org/show_bug.cgi?id=105406">bug 105406</a>
from <span class="vcard"><a class="email" href="mailto:peteris.rudzusiks@gmail.com" title="Peteris <peteris.rudzusiks@gmail.com>"> <span class="fn">Peteris</span></a>
</span></b>
<pre>I have a POS computer that also uses CH7511. Just like in David's case, the
internal display of the POS is broken with Linux kernels 4.5+. The display
shows no output. I can confirm that commit 30d9aa4265fe is the first commit
since v4.4 that does not work.
For what it's worth, here is a patch for v4.19.35 that fixes the problem for
me. Not sure if this is a proper fix or hacky workaround for broken hardware,
but it works for me and maybe someone else finds it useful.
---
drivers/gpu/drm/i915/intel_dp.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index f92079e19de8..ec908f605708 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3840,6 +3840,9 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
*/
intel_dp->sink_count = DP_GET_SINK_COUNT(sink_count);
+ if (!drm_dp_is_branch(intel_dp->dpcd))
+ return true; /* native DP sink */
+
/*
* SINK_COUNT == 0 and DOWNSTREAM_PORT_PRESENT == 1 implies that
* a dongle is present but no display. Unless we require to know
@@ -3850,9 +3853,6 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp)
if (!intel_dp_is_edp(intel_dp) && !intel_dp->sink_count)
return false;
- if (!drm_dp_is_branch(intel_dp->dpcd))
- return true; /* native DP sink */
-
if (intel_dp->dpcd[DP_DPCD_REV] == 0x10)
return true; /* no per-port downstream info */
--
2.17.1
The CH7511 is not a branch device according to DPCD, so intel_dp_get_dpcd()
function will return without actually using the incorrect SINK_COUNT variable.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are the assignee for the bug.</li>
<li>You are on the CC list for the bug.</li>
<li>You are the QA Contact for the bug.</li>
</ul>
</body>
</html>