[PATCH v2] drm: add docs for standard CRTC properties

[Simon Ser]

This patch adds docs for the ACTIVE and MODE_ID CRTC properties.

Signed-off-by: Simon Ser <contact at emersion.fr>
Cc: Daniel Vetter <daniel.vetter at intel.com>
Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
Cc: Pekka Paalanen <pekka.paalanen at collabora.co.uk>
Cc: Michel Dänzer <michel at daenzer.net>
Cc: Daniel Stone <daniel at fooishbar.org>
---

Thanks for the review Daniel! I rejiggered your suggestions a little to
move some ACTIVE bits into the ACTIVE description.

 Documentation/gpu/drm-kms.rst |  6 ++++++
 drivers/gpu/drm/drm_crtc.c    | 27 +++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst
index 397314d08f77..975cfeb8a353 100644
--- a/Documentation/gpu/drm-kms.rst
+++ b/Documentation/gpu/drm-kms.rst
@@ -460,6 +460,12 @@ HDMI Specific Connector Properties
 .. kernel-doc:: drivers/gpu/drm/drm_connector.c
    :doc: HDMI connector properties
 
+Standard CRTC Properties
+------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_crtc.c
+   :doc: standard CRTC properties
+
 Plane Composition Properties
 ----------------------------
 
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 4936e1080e41..fafb8d3c3235 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -204,6 +204,33 @@ struct dma_fence *drm_crtc_create_fence(struct drm_crtc *crtc)
 	return fence;
 }
 
+/**
+ * DOC: standard CRTC properties
+ *
+ * DRM CRTCs have a few standardized properties:
+ *
+ * ACTIVE:
+ * 	Atomic property for setting the power state of the CRTC. When set to 1 the
+ * 	CRTC will actively display content. When set to 0 the CRTC will be powered
+ * 	off. There is no expectation that user-space will reset CRTC resources like
+ * 	the mode and planes when setting ACTIVE to 0.
+ *
+ * 	User-space can rely on an ACTIVE change to 1 to never fail an atomic test
+ * 	as long as no other property has changed. If a change to ACTIVE fails an
+ * 	atomic test, this is a driver bug. For this reason setting ACTIVE to 0 must
+ * 	not release internal resources (like reserved memory bandwidth or clock
+ * 	generators).
+ *
+ * 	Note that the legacy DPMS property on connectors is internally routed to
+ * 	control this property for atomic drivers.
+ * MODE_ID:
+ * 	Atomic property for setting the CRTC display timings. The value is the ID
+ * 	of a blob containing the DRM mode info. To disable the CRTC, user-space
+ * 	must set this property to 0.
+ *
+ * 	Setting MODE_ID to 0 will release reserved resources for the CRTC.
+ */
+
 /**
  * drm_crtc_init_with_planes - Initialise a new CRTC object with
  *    specified primary and cursor planes.
-- 
2.26.2