From: Imre Deak Date: Tue, 1 Apr 2025 10:38:45 +0000 (+0300) Subject: drm/dp_mst: Fix GUID DPCD write to non-root MST branch devices X-Git-Tag: v6.16-rc1~33^2~30^2~66 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=aea007741b951df05f901b2d4890df2e710d134b;p=linux-block.git drm/dp_mst: Fix GUID DPCD write to non-root MST branch devices The return value on success of drm_dp_send_dpcd_write() called for non-root MST branch devices from drm_dp_check_mstb_guid() is the number of bytes transferred. Atm this return value (in case of a complete read) will be regarded incorrectly as an error by the caller of drm_dp_check_mstb_guid(). Fix this by converting the return value for a complete read to the expected success code (0) and for a partial read to a failure code (-EPROTO). Fixes: 2554da0de3e8 ("drm/display: dp-mst-topology: use new DCPD access helpers") Cc: Dmitry Baryshkov Cc: Lyude Paul Reviewed-by: Jani Nikula Reviewed-by: Lyude Paul Signed-off-by: Imre Deak Link: https://lore.kernel.org/r/20250401103846.686408-1-imre.deak@intel.com --- diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c b/drivers/gpu/drm/display/drm_dp_mst_topology.c index e8716e73480b..8c312c1f1724 100644 --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c @@ -2200,6 +2200,8 @@ static int drm_dp_check_mstb_guid(struct drm_dp_mst_branch *mstb, guid_t *guid) ret = drm_dp_send_dpcd_write(mstb->mgr, mstb->port_parent, DP_GUID, sizeof(buf), buf); + if (ret >= 0) + ret = ret == sizeof(buf) ? 0 : -EPROTO; } else { ret = drm_dp_dpcd_write_data(mstb->mgr->aux, DP_GUID, buf, sizeof(buf));