[PATCH v2] drm: Clarify DRM_MODE_REFLECT_X/Y documentation

[Ville Syrjälä]

On Mon, Sep 10, 2018 at 06:29:46PM +0100, Alexandru Gheorghe wrote:
> DRM_MODE_REFLECT_X and DRM_MODE_REFLECT_Y meaning seems a bit unclear
> to me, so try to clarify that with a bit of ascii graphics.
> 
> Changes since v1:
>   - Move the ascii graphics in the kerneldoc where all plane
>     properties are already documented and make sure it's properly
>     rendered, suggestested by Daniel Vetter.
> 
> Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe at arm.com>
> ---
>  drivers/gpu/drm/drm_blend.c | 22 ++++++++++++++++++++++
>  include/uapi/drm/drm_mode.h |  3 ++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_blend.c b/drivers/gpu/drm/drm_blend.c
> index 402b62d3f072..92f75c5c93ac 100644
> --- a/drivers/gpu/drm/drm_blend.c
> +++ b/drivers/gpu/drm/drm_blend.c
> @@ -101,6 +101,28 @@
>   *	Without this property the rectangle is only scaled, but not rotated or
>   *	reflected.
>   *
> + *	Possbile values:
> + *
> + *	"rotate-<degrees>":
> + *		Signals that a drm plane is rotated <degrees> degrees in counter
> + *		clockwise direction.
> + *
> + *	"reflect-<axis>":
> + *		Signals that the contents of a drm plane is reflected along the
> + *		<axis> axis, in the same way as mirroring.

What does "mirroring" mean? Feels like a circular definition here.

Also the relationship between rotate and reflect is missing from these
docs. The order matters, and I do believe we have it specified in some
comment somewhere. Would be good to include it here as well.

> + *
> + *	reflect-x::
> + *
> + *			|o |    | o|
> + *			|  | -> |  |
> + *			| v|    |v |
> + *
> + * 	reflect-y::
> + *
> + *			|o |    | ^|
> + *			|  | -> |  |
> + *			| v|    |o |
> + *
>   * zpos:
>   *	Z position is set up with drm_plane_create_zpos_immutable_property() and
>   *	drm_plane_create_zpos_property(). It controls the visibility of overlapping
> diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> index 8d67243952f4..d3e0fe31efc5 100644
> --- a/include/uapi/drm/drm_mode.h
> +++ b/include/uapi/drm/drm_mode.h
> @@ -186,8 +186,9 @@ extern "C" {
>  /*
>   * DRM_MODE_REFLECT_<axis>
>   *
> - * Signals that the contents of a drm plane is reflected in the <axis> axis,
> + * Signals that the contents of a drm plane is reflected along the <axis> axis,
>   * in the same way as mirroring.
> + * See kerneldoc chapter "Plane Composition Properties" for more details.
>   *
>   * This define is provided as a convenience, looking up the property id
>   * using the name->prop id lookup is the preferred method.
> -- 
> 2.18.0
> 
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-- 
Ville Syrjälä
Intel