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Feedback-ID: i8771445c:Fastmail
Date:   Mon, 23 Oct 2023 16:58:12 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Hans Verkuil <hverkuil@xs4all.nl>
Cc:     Daniel Vetter <daniel@ffwll.ch>, Emma Anholt <emma@anholt.net>,
        David Airlie <airlied@gmail.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dave Stevenson <dave.stevenson@raspberrypi.com>
Subject: Re: [PATCH v3 3/9] drm/vc4: hdmi: Add Broadcast RGB property to
 allow override of RGB range
Message-ID: <tnkfcgkoobxyyhnsmoyayohip73wl6axnd7liefsvof6qwgovd@ropob4set3nl>
References: <20221207-rpi-hdmi-improvements-v3-0-bdd54f66884e@cerno.tech>
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Hi Hans,

On Thu, Oct 19, 2023 at 10:26:40AM +0200, Hans Verkuil wrote:
> Hi Maxime,
>=20
> On 19/10/2023 10:02, Maxime Ripard wrote:
> > Hi,
> >=20
> > On Wed, Oct 11, 2023 at 03:23:18PM +0200, Daniel Vetter wrote:
> >> On Mon, 6 Mar 2023 at 11:49, Maxime Ripard <maxime@cerno.tech> wrote:
> >>>
> >>> From: Dave Stevenson <dave.stevenson@raspberrypi.com>
> >>>
> >>> Copy Intel's "Broadcast RGB" property semantics to add manual override
> >>> of the HDMI pixel range for monitors that don't abide by the content
> >>> of the AVI Infoframe.
> >>>
> >>> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> >>> Signed-off-by: Maxime Ripard <maxime@cerno.tech>
> >>
> >> Stumbled over this grepping around, but would have been nice to lift
> >> this into drm code and document the property. It's one of the legacy
> >> ones from the table of horrors after all ...
> >>
> >> Shouldn't be an uapi problem because it's copypasted to much, just not=
 great.
> >=20
> > We already discussed it on IRC, but just for the record I have a current
> > series that should address exactly that:
> >=20
> > https://lore.kernel.org/dri-devel/20230920-kms-hdmi-connector-state-v2-=
3-17932daddd7d@kernel.org/
> >=20
> > Maxime
>=20
> I've pasted a snippet from that patch below for a quick review:
>=20
> >  /**
> >   * DOC: HDMI connector properties
> >   *
> > + * Broadcast RGB (HDMI Specific):
>=20
> Full vs Limited is actually not HDMI specific, DisplayPort can signal thi=
s as
> well for whatever it is worth.

Sure, what I (and the original patch I guess) meant is that it's only
ever used on HDMI connectors these days. If that ever changes, then we
can update the doc.

> > + *      Indicates the RGB Range (Full vs Limited) used.
>=20
> RGB Range -> RGB Quantization Range
>=20
> > + *
> > + *      The value of this property can be one of the following:
> > + *
> > + *      Automatic:
> > + *              RGB Range is selected automatically based on the mode
> > + *              according to the HDMI specifications.
> > + *
> > + *      Full:
> > + *              Full RGB Range is forced.
> > + *
> > + *      Limited 16:235:
>=20
> It is very unfortunate that this is called "Limited 16:235" instead of ju=
st "Limited"
> since for color component bit depths > 8 these values are different.
>=20
> I have no idea if it is possible to add an alias "Limited" that you can u=
se instead.
> In any case, this should document that it works just as well for higher b=
it depths,
> but with different limits.

I had a look and it doesn't look like the property infrastructure can
deal with aliases. I'll add something in the doc

Thanks!
Maxime

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