linux-kernel - Re: [PATCH v2 2/2] dt-bindings: display: simple-framebuffer: Document physical width and height properties

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Message-ID: <cdf32cb0-4529-6bbd-fdda-ae641d141ee5@ansari.sh>
Date:   Sun, 22 Jan 2023 17:25:38 +0000
From:   Rayyan Ansari <rayyan@...ari.sh>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     dri-devel@...ts.freedesktop.org,
        ~postmarketos/upstreaming@...ts.sr.ht, asahi@...ts.linux.dev,
        janne@...nau.net, Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>, devicetree@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH v2 2/2] dt-bindings: display: simple-framebuffer: Document
 physical width and height properties

On 22/01/2023 15:36, Rob Herring wrote:
> On Sat, Jan 21, 2023 at 9:36 AM Rayyan Ansari <rayyan@...ari.sh> wrote:
>>
> 
> Why do you need this change?
> 
> The 'simple-framebuffer' contains data on how the bootloader
> configured the display. The bootloader doesn't configure the display
> size, so this information doesn't belong here. The information should
> already be in the panel node, so also no point in duplicating it here.
> 
>> Signed-off-by: Rayyan Ansari <rayyan@...ari.sh>
>> ---
>>   .../devicetree/bindings/display/simple-framebuffer.yaml   | 8 ++++++++
>>   1 file changed, 8 insertions(+)

Hi Rob,

There is the usecase that Hans has mentioned, but I have also mentioned 
another usecase previously.

Adding the width-mm and height-mm properties allows user interfaces such 
as Phosh (https://puri.sm/posts/phosh-overview/) to scale correctly to 
the screen. In my case, a panel node is not available and the 
aforementioned interface is in fact running on the SimpleDRM driver 
(which binds to the simple-framebuffer device).

Here is the device I have tested this patch on, the Lumia 735 phone: 
https://wiki.postmarketos.org/images/c/c3/Lumia_735_Phosh.png
Without this patch, this would appear quite small on the screen.

See https://patchwork.freedesktop.org/patch/519107/?series=113053&rev=1 
for some background info about this patch.

Regards,
-- 
Rayyan Ansari
https://ansari.sh