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@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+ > --- > 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. > + */ > len = drm_dp_downstream_port_count(dpcd); > + if (!len) > + return 0; > + Seems sane enough. Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > if (dpcd[DP_DOWNSTREAMPORT_PRESENT] & DP_DETAILED_CAP_INFO_AVAILABLE) > len *= 4; > > -- > 2.30.2 > > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Ville Syrjälä Intel
