drm/dp: Fix bogus DPCD version check in drm_dp_read_downstream_info()

Ville pointed this out to me when fixing some issues in
drm_dp_read_downstream_info() - the DPCD version check here is bogus as
there's no DisplayPort versions prior to 1.0. The original code from i915
that this was extracted from actually did:

  dpcd[DP_DPCD_REV] == DP_DPCD_REV_10

Which is correct, and somehow got missed when extracting this function. So
let's fix this. Note that as far as I'm aware, I don't think this fixes any
actual issues users are hitting.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210507214209.554866-1-lyude@redhat.com

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 0f84df8..55b53df 100644 (file)
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -677,7 +677,7 @@ int drm_dp_read_downstream_info(struct drm_dp_aux *aux,
        memset(downstream_ports, 0, DP_MAX_DOWNSTREAM_PORTS);
 
        /* No downstream info to read */
-       if (!drm_dp_is_branch(dpcd) || dpcd[DP_DPCD_REV] < DP_DPCD_REV_10)
+       if (!drm_dp_is_branch(dpcd) || dpcd[DP_DPCD_REV] == DP_DPCD_REV_10)
                return 0;
 
        /* Some branches advertise having 0 downstream ports, despite also advertising they have a