Daniel Vetter <daniel.vetter@xxxxxxxx> writes: > Laurent asked for this. > > Cc: Laurent Pinchart <laurent.pinchart+renesas@xxxxxxxxxxxxxxxx> > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > --- > 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 s/relevant/defined/ maybe? > + * 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". Maybe another newline here? > + * 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. Maybe add " on legacy drivers"? > + * > + * 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 "also sets" > + * read back the value of "DPMS" because it can be incorrect. With whatever set of my suggestions you like, Reviewed-by: Eric Anholt <eric@xxxxxxxxxx>
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