On Fri, Apr 30, 2021 at 06:34:27PM -0400, Lyude Paul wrote:
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+
drivers/gpu/drm/drm_dp_helper.c | 7 +++++++ 1 file changed, 7 insertions(+)
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.*/- if (!len)
return 0;
Seems sane enough.
Reviewed-by: Ville Syrjälä ville.syrjala@linux.intel.com
if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE) len *= 4; -- 2.30.2
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