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| author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2017-09-21 00:59:57 +0200 |
|---|---|---|
| committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2017-09-26 07:12:56 +0200 |
| commit | d0d1aee5f7eda2f2cae0932a217e27493f2c2faa (patch) | |
| tree | 54eb04d5f731f17878da9e3d46f29a45b7d7200d /drivers/gpu/drm/drm_connector.c | |
| parent | 6bf2e0324b9376512b0b9bf5c5c4b383afd419ec (diff) | |
| download | lwn-d0d1aee5f7eda2f2cae0932a217e27493f2c2faa.tar.gz lwn-d0d1aee5f7eda2f2cae0932a217e27493f2c2faa.zip | |
drm: Try to document legacy DPMS uapi a bit better
Due to inconsistency of how various legacy drivers implemented DPMS
the DPMS uabi has a lot of quirks. Atomic standardizes this, but
drivers using the DPMS support can't rely on that since legacy drivers
still exist.
Laurent asked for this.
v2:
Improve commit message and explain that DPMS doesn't really exist for
the atomic ioctl (it's "ACTIVE" on the CRTC instead).
Text polish from Eric's review.
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20170920225957.16278-1-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/gpu/drm/drm_connector.c')
| -rw-r--r-- | drivers/gpu/drm/drm_connector.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index bb2e60f5feb6..d8ca526ca4ee 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -719,6 +719,29 @@ 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. + * + * Note that this property cannot be set through the MODE_ATOMIC ioctl, + * userspace must use "ACTIVE" on the CRTC instead. + * + * 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 well-defined 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 on legacy drivers. + * + * Summarizing: Only set "DPMS" when the connector is known to be enabled, + * assume that a successful SETCONFIG call also sets "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 |