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Date:   Wed, 29 Mar 2023 11:16:36 +0200
From:   Maxime Ripard <maxime@cerno.tech>
To:     Michael Riesch <michael.riesch@wolfvision.net>
Cc:     Rob Herring <robh@kernel.org>,
        Gerald Loacker <gerald.loacker@wolfvision.net>,
        dri-devel@lists.freedesktop.org, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Thierry Reding <thierry.reding@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>
Subject: Re: [PATCH 7/7] dt-bindings: display: add panel-timing property to
 sitronix,st7789v
Message-ID: <20230329091636.mu6ml3gvw5mvkhm4@penduick>
References: <20230314115644.3775169-1-gerald.loacker@wolfvision.net>
 <20230314115644.3775169-8-gerald.loacker@wolfvision.net>
 <20230316215735.GA3940832-robh@kernel.org>
 <dd26836f-d54c-65d1-0acc-8a09745bb066@wolfvision.net>
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On Thu, Mar 16, 2023 at 11:29:53PM +0100, Michael Riesch wrote:
> Hi Rob,
>=20
> On 3/16/23 22:57, Rob Herring wrote:
> > On Tue, Mar 14, 2023 at 12:56:44PM +0100, Gerald Loacker wrote:
> >> The sitronix-st7789v driver now considers the panel-timing property.
> >=20
> > I read the patch for that and still don't know 'why'. Commit messages=
=20
> > should answer why.
> >=20
> >> Add the property to the documentation.
> >=20
> > We generally don't put timings in DT for panels. Why is this one=20
> > special?
>=20
> For now, having the timings in the device tree allows for setting the
> hsync/vsync/de polarity.
>=20
> As a next step, we aim to implement the partial mode feature of this
> panel. It is possible to use only a certain region of the panel, which
> is helpful e.g., when a part of the panel is occluded and should not be
> considered by DRM. We thought that this could be specified as timing in D=
T.
>
> (The hactive and vactive properties serve as dimensions of this certain
> region, of course. We still need to specify somehow the position of the
> region. Maybe with additional properties hactive-start and vactive-start?)
>=20
> What do you think about that?

I don't see why we would need the device tree to support that. What you
described is essentially what overscan is for HDMI/analog output, and we
already have everything to deal with overscan properly in KMS.

Maxime