On Fri, May 07, 2021 at 05:42:09PM -0400, Lyude Paul wrote:

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

---

drivers/gpu/drm/drm_dp_helper.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 0f84df8798ab..55b53df6ce34 100644 --- 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

-- 2.30.2