drm/color: document NULL values and default settings better

Brought up in a discussion for enabling gamma on fsl-dcu.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Meng Yi <meng.yi@nxp.com>
Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20160926090437.22676-1-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/drm_color_mgmt.c b/drivers/gpu/drm/drm_color_mgmt.c
index d28ffdd..6543ebd 100644 (file)
--- a/drivers/gpu/drm/drm_color_mgmt.c
+++ b/drivers/gpu/drm/drm_color_mgmt.c
@@ -41,6 +41,10 @@
  *     nor use all the elements of the LUT (for example the hardware might
  *     choose to interpolate between LUT[0] and LUT[4]).
  *
+ *     Setting this to NULL (blob property value set to 0) means a
+ *     linear/pass-thru gamma table should be used. This is generally the
+ *     driver boot-up state too.
+ *
  * “DEGAMMA_LUT_SIZE”:
  *     Unsinged range property to give the size of the lookup table to be set
  *     on the DEGAMMA_LUT property (the size depends on the underlying
@@ -54,6 +58,10 @@
  *     lookup through the gamma LUT. The data is interpreted as a struct
  *     &drm_color_ctm.
  *
+ *     Setting this to NULL (blob property value set to 0) means a
+ *     unit/pass-thru matrix should be used. This is generally the driver
+ *     boot-up state too.
+ *
  * “GAMMA_LUT”:
  *     Blob property to set the gamma lookup table (LUT) mapping pixel data
  *     after the transformation matrix to data sent to the connector. The
@@ -62,6 +70,10 @@
  *     nor use all the elements of the LUT (for example the hardware might
  *     choose to interpolate between LUT[0] and LUT[4]).
  *
+ *     Setting this to NULL (blob property value set to 0) means a
+ *     linear/pass-thru gamma table should be used. This is generally the
+ *     driver boot-up state too.
+ *
  * “GAMMA_LUT_SIZE”:
  *     Unsigned range property to give the size of the lookup table to be set
  *     on the GAMMA_LUT property (the size depends on the underlying hardware).