linux-kernel - Re: [PATCH 1/5] dt-bindings: display: panel: samsung,atna33xc20: Document ATNA45AF01

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Message-ID: <CAD=FV=U_knZPsM3jnpUOqK7rcBjJeqPAHDG9QRgWhLVeKGZwGg@mail.gmail.com>
Date: Wed, 10 Jul 2024 12:16:58 -0700
From: Doug Anderson <dianders@...omium.org>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
Cc: Neil Armstrong <neil.armstrong@...aro.org>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, Jessica Zhang <quic_jesszhan@...cinc.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org, 
	Abel Vesa <abel.vesa@...aro.org>, Johan Hovold <johan@...nel.org>
Subject: Re: [PATCH 1/5] dt-bindings: display: panel: samsung,atna33xc20:
 Document ATNA45AF01

Hi,

On Wed, Jul 10, 2024 at 12:03 PM Stephan Gerhold
<stephan.gerhold@...aro.org> wrote:
>
> > 2. In theory you could make your compatible look like this:
> >
> > compatible = "samsung,atna45af01", "samsung,atna33xc20"
> >
> > ...which would say "I have a 45af01 but if the OS doesn't have
> > anything special to do that it would be fine to use the 33xc20
> > driver". That would allow device trees to work without the kernel
> > changes and would allow you to land the DT changes in parallel with
> > the driver changes and things would keep working.
> >
> > ...and, in fact, that would mean you _didn't_ need to add the new
> > compatible string to the driver, which is nice.
> >
>
> Yeah, I considered this. I mentioned the reason why I decided against
> this in patch 2:
>
> > While ATNA45AF01 would also work with "samsung,atna33xc20" as a fallback
> > compatible, the original submission of the compatible in commit
> > 4bfe6c8f7c23 ("drm/panel-simple: Add Samsung ATNA33XC20") had the timings
> > and resolution hardcoded. These would not work for ATNA45AF01.
>
> Basically, it works with the current driver. But if you would run the
> kernel at the state of the original submission then it would behave
> incorrectly. This is why I considered the resolution and timings to be
> part of the "samsung,atna33xc20" "ABI". The new panel would not be
> compatible with that.

Ah, oops. My eyes totally glazed over the description since the patch
was so simple. :-P Sorry about that.

IMO I'd still prefer using the fallback compatible, but happy to hear
other opinions. In the original commit things were pretty broken still
(sorta like how it's broken for you using "edp-panel") and the
resolution hasn't been hardcoded for a long while...