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 5.13-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-5.13 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 Content-Transfer-Encoding: 8bit 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 @@ -679,7 +679,14 @@ 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-5.13/drm-msm-mdp4-fix-modifier-support-enabling.patch queue-5.13/drm-dp_mst-do-not-set-proposed-vcpi-directly.patch queue-5.13/drm-arm-malidp-always-list-modifiers.patch queue-5.13/drm-dp-handle-zeroed-port-counts-in-drm_dp_read_downstream_info.patch queue-5.13/drm-nouveau-don-t-set-allow_fb_modifiers-explicitly.patch