linux-kernel - Re: [PATCH v7 21/36] drm/connector: hdmi: Add Broadcast RGB property

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Message-ID: <20240301112941.GE166694@toolbox>
Date: Fri, 1 Mar 2024 12:29:41 +0100
From: Sebastian Wick <sebastian.wick@...hat.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Jonathan Corbet <corbet@....net>, Sandy Huang <hjc@...k-chips.com>,
	Heiko Stübner <heiko@...ech.de>,
	Chen-Yu Tsai <wens@...e.org>,
	Jernej Skrabec <jernej.skrabec@...il.com>,
	Samuel Holland <samuel@...lland.org>,
	Hans Verkuil <hverkuil@...all.nl>,
	Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	dri-devel@...ts.freedesktop.org,
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
	linux-rockchip@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
	Dave Stevenson <dave.stevenson@...pberrypi.com>
Subject: Re: [PATCH v7 21/36] drm/connector: hdmi: Add Broadcast RGB property

On Fri, Mar 01, 2024 at 11:30:56AM +0100, Maxime Ripard wrote:
> On Thu, Feb 29, 2024 at 08:47:26PM +0100, Sebastian Wick wrote:
> > > @@ -1708,6 +1731,39 @@ EXPORT_SYMBOL(drm_connector_attach_dp_subconnector_property);
> > >  /**
> > >   * DOC: HDMI connector properties
> > >   *
> > > + * Broadcast RGB (HDMI specific)
> > > + *      Indicates the Quantization Range (Full vs Limited) used. The color
> > > + *      processing pipeline will be adjusted to match the value of the
> > > + *      property, and the Infoframes will be generated and sent accordingly.
> > > + *
> > > + *      This property is only relevant if the HDMI output format is RGB. If
> > > + *      it's one of the YCbCr variant, it will be ignored and the output will
> > > + *      use a limited quantization range.
> > 
> > Uh, maybe just say that the quantization range is selected automatically
> > in case a YCbCr output format is in use. I'm not sure every YCbCr
> > variant requires limited and even if it does, new formats could change
> > this.
> 
> I documented what i915 is doing:
> https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/i915/display/intel_hdmi.c#L2143

Sure, this is one valid strategy for the automatic behavior of YCbCr.
Drivers could also always send an InfoFrame to ensure full range where
possible. The point here is that this property shall not affect YCbCr
output formats!

Maybe it's even better to say "driver specific" instead of "automatic".

> Maxime
>