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| author | Lyude Paul <lyude@redhat.com> | 2021-04-30 18:34:27 -0400 |
|---|---|---|
| committer | Lyude Paul <lyude@redhat.com> | 2021-05-07 17:32:22 -0400 |
| commit | 205bb69a90363541a634a662a599fddb95956524 (patch) | |
| tree | 69b85745250e84c47781966cada4ffadf5ae5135 | |
| parent | 767d724a160eb1cd00c86fb8c2e21fa1ab3c37ac (diff) | |
| download | linux-205bb69a90363541a634a662a599fddb95956524.tar.bz2 | |
drm/dp: Handle zeroed port counts in drm_dp_read_downstream_info()
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@redhat.com>
Tested-by: Jérôme de Bretagne <jerome.debretagne@gmail.com>
Bugzilla: https://gitlab.freedesktop.org/drm/intel/-/issues/3416
Fixes: 3d3721ccb18a ("drm/i915/dp: Extract drm_dp_read_downstream_info()")
Cc: <stable@vger.kernel.org> # v5.10+
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210430223428.10514-1-lyude@redhat.com
| -rw-r--r-- | drivers/gpu/drm/drm_dp_helper.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index cb56d74e9d38..27c8c5bdf7d9 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -682,7 +682,14 @@ int drm_dp_read_downstream_info(struct drm_dp_aux *aux, !(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; |