Laurent asked for this. Cc: Laurent Pinchart <laurent.pinchart+rene...@ideasonboard.com> Signed-off-by: Daniel Vetter <daniel.vet...@intel.com> --- drivers/gpu/drm/drm_connector.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+)
diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index ba9f36cef68c..b458eb488128 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -720,6 +720,25 @@ DRM_ENUM_NAME_FN(drm_get_tv_subconnector_name, * callback. For atomic drivers the remapping to the "ACTIVE" property is * implemented in the DRM core. This is the only standard connector * property that userspace can change. + * + * WARNING: + * + * For userspace also running on legacy drivers the "DPMS" semantics are a + * lot more complicated. First, userspace cannot rely on the "DPMS" value + * returned by the GETCONNECTOR actually reflecting reality, because many + * drivers fail to update it. For atomic drivers this is taken care of in + * drm_atomic_helper_update_legacy_modeset_state(). + * + * The second issue is that the DPMS state is only relevant when the + * connector is connected to a CRTC. In atomic the DRM core enforces that + * "ACTIVE" is off in such a case, no such checks exists for "DPMS". + * Finally, when enabling an output using the legacy SETCONFIG ioctl then + * "DPMS" is forced to ON. But see above, that might not be reflected in + * the software value. + * + * Summarizing: Only set "DPMS" when the connector is known to be enabled, + * assume that a successful SETCONFIG call also set "DPMS" to on, and never + * read back the value of "DPMS" because it can be incorrect. * PATH: * Connector path property to identify how this sink is physically * connected. Used by DP MST. This should be set by calling -- 2.13.3 _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
