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

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Message-ID: <097de164-6d62-6a1d-f7b5-cbd7d4408ab7@wolfvision.net>
Date:   Wed, 2 Aug 2023 14:34:28 +0200
From:   Michael Riesch <michael.riesch@...fvision.net>
To:     Maxime Ripard <mripard@...nel.org>
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 Maxime,

On 7/19/23 08:39, Maxime Ripard wrote:
> Hi,
> 
> 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?

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

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.

Thanks and best regards,
Michael

> 
> Maxime