This is a note to let you know that I've just added the patch titled
drm/dp: Handle zeroed port counts in drm_dp_read_downstream_info()
to the 5.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-dp-handle-zeroed-port-counts-in-drm_dp_read_downstream_info.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 205bb69a90363541a634a662a599fddb95956524 Mon Sep 17 00:00:00 2001
From: Lyude Paul <lyude@xxxxxxxxxx>
Date: Fri, 30 Apr 2021 18:34:27 -0400
Subject: drm/dp: Handle zeroed port counts in drm_dp_read_downstream_info()
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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From: Lyude Paul <lyude@xxxxxxxxxx>
commit 205bb69a90363541a634a662a599fddb95956524 upstream.
While the DP specification isn't entirely clear on if this should be
allowed or not, some branch devices report having downstream ports present
while also reporting a downstream port count of 0. So to avoid breaking
those devices, we need to handle this in drm_dp_read_downstream_info().
So, to do this we assume there's no downstream port info when the
downstream port count is 0.
Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
Tested-by: Jérôme de Bretagne <jerome.debretagne@xxxxxxxxx>
Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/3416
Fixes: 3d3721ccb18a ("drm/i915/dp: Extract drm_dp_read_downstream_info()")
Cc: <stable@xxxxxxxxxxxxxxx> # v5.10+
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20210430223428.10514-1-lyude@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_dp_helper.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -602,7 +602,14 @@ int drm_dp_read_downstream_info(struct d
!(dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DWN_STRM_PORT_PRESENT))
return 0;
+ /* Some branches advertise having 0 downstream ports, despite also advertising they have a
+ * downstream port present. The DP spec isn't clear on if this is allowed or not, but since
+ * some branches do it we need to handle it regardless.
+ */
len = drm_dp_downstream_port_count(dpcd);
+ if (!len)
+ return 0;
+
if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE)
len *= 4;
Patches currently in stable-queue which might be from lyude@xxxxxxxxxx are
queue-5.10/drm-msm-mdp4-fix-modifier-support-enabling.patch
queue-5.10/drm-dp_mst-do-not-set-proposed-vcpi-directly.patch
queue-5.10/drm-arm-malidp-always-list-modifiers.patch
queue-5.10/drm-dp-handle-zeroed-port-counts-in-drm_dp_read_downstream_info.patch
queue-5.10/drm-nouveau-don-t-set-allow_fb_modifiers-explicitly.patch
