linux-kernel - Re: [PATCH 3/4] drm/panel: sitronix-st7789v: add support for partial mode

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Message-ID: <jfmsb4tmgx5rej4ae4npzq4zjh2dnydukxuk34oejbqdpe4a42@a2bbo3bwa3yq>
Date:   Wed, 2 Aug 2023 14:47:04 +0200
From:   Maxime Ripard <mripard@...nel.org>
To:     Michael Riesch <michael.riesch@...fvision.net>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Sam Ravnborg <sam@...nborg.org>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Sebastian Reichel <sre@...nel.org>,
        Gerald Loacker <gerald.loacker@...fvision.net>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 3/4] drm/panel: sitronix-st7789v: add support for partial
 mode

Hi,

On Wed, Aug 02, 2023 at 02:34:28PM +0200, Michael Riesch wrote:
> On 7/19/23 08:39, Maxime Ripard wrote:
> > On Tue, Jul 18, 2023 at 05:31:52PM +0200, Michael Riesch wrote:
> >> The ST7789V controller features support for the partial mode. Here,
> >> the area to be displayed can be restricted in one direction (by default,
> >> in vertical direction). This is useful for panels that are partially
> >> occluded by design. Add support for the partial mode.
> >>
> >> Signed-off-by: Michael Riesch <michael.riesch@...fvision.net>
> > 
> > We already had that discussion, but I think we shouldn't treat this any
> > differently than overscan for other output.
> 
> Indeed we had that discussion. For reference, it can be found here:
> https://lore.kernel.org/dri-devel/20230329091636.mu6ml3gvw5mvkhm4@penduick/#t
> The thing is that I am still clueless how the overscan approach could work.
> 
> I found some DRM properties related to overscan/margins and I guess
> userspace needs to set those. On my system weston is running. Is weston
> in charge of configuring the corresponding output so that the correct
> margins are applied? If so, how can this be achieved?

I don't really know Weston, but my guess would be based on some
configuration or user feedback, depending on which case we're in.

We also set the default using some kernel command-line options.

> Will DRM handle the properties generically or does the driver need to do
> some work as well?

What do you mean by generically?

> In any case it could make sense to write the partial mode registers and
> enter the effective dimensions. At least I have seen this in other panel
> drivers.

Sure, it makes sense. It shouldn't come from the DT and be fixed though.

Maxime

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