[PATCH v2] drm: document connector margin properties

[Ville Syrjälä]

On Tue, Feb 28, 2023 at 12:32:04PM +0000, Simon Ser wrote:
> Add docs for "{left,right,top,bottom} margin" properties.
> 
> v2:
> - Mention the purpose: mitigate underscan on TVs
> - Move out of analog TV section into standard props (Pekka)
> - Mention HDMI AVI InfoFrames (Pekka, Ville)
> 
> Signed-off-by: Simon Ser <contact at emersion.fr>
> Cc: Maxime Ripard <maxime at cerno.tech>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Cc: Pekka Paalanen <ppaalanen at gmail.com>
> Cc: Noralf Trønnes <noralf at tronnes.org>
> Cc: Mateusz Kwiatkowski <kfyatek+publicgit at gmail.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_connector.c | 18 ++++++++++++++----
>  1 file changed, 14 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> index ffd65eddce42..a180f541736a 100644
> --- a/drivers/gpu/drm/drm_connector.c
> +++ b/drivers/gpu/drm/drm_connector.c
> @@ -1446,6 +1446,20 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
>   *	a firmware handled hotkey. Therefor userspace must not include the
>   *	privacy-screen sw-state in an atomic commit unless it wants to change
>   *	its value.
> + *
> + * left margin, right margin, top margin, bottom margin:
> + *	Add margins to the connector's viewport. This is typically used to
> + *	mitigate underscan on TVs.

"used to mitigate overscan" or "used to underscan" would make
more sense to me.

> + *
> + *	The value is the size in pixels of the black border which will be
> + *	added. The attached CRTC's content will be scaled to fill the whole
> + *	area inside the margin.

Dunno if there should be something even more explicit here
about the CRTCs viewport/canvas/<whatever you call it> size
remaining unchaned, ie. still 'hdisplay x vdisplay'?

Another very open question is how these would interact with
the 'scaling mode' property/connectors that already scale
the passed in mode to whatever fixed size the panel needs.
In my i915 patches I totally sidestepped that question by
not registering the margin properties for eDP at all.

-- 
Ville Syrjälä
Intel