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

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Message-ID: <Zo7a6qso7RZ2pkmb@linaro.org>
Date: Wed, 10 Jul 2024 21:03:06 +0200
From: Stephan Gerhold <stephan.gerhold@...aro.org>
To: Doug Anderson <dianders@...omium.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

On Wed, Jul 10, 2024 at 10:35:28AM -0700, Doug Anderson wrote:
> On Wed, Jul 10, 2024 at 10:05 AM Stephan Gerhold
> <stephan.gerhold@...aro.org> wrote:
> >
> > The Samsung ATNA45AF01 panel is an AMOLED eDP panel that has backlight
> > control over the DP AUX channel. While it works almost correctly with the
> > generic "edp-panel" compatible, the backlight needs special handling to
> > work correctly. It is similar to the existing ATNA33XC20 panel, just with
> > a larger resolution and size.
> >
> > Add a new "samsung,atna45af01" compatible to describe this panel in the DT.
> >
> > Signed-off-by: Stephan Gerhold <stephan.gerhold@...aro.org>
> > ---
> >  .../devicetree/bindings/display/panel/samsung,atna33xc20.yaml       | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml b/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
> > index 765ca155c83a..d668e8d0d296 100644
> > --- a/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
> > +++ b/Documentation/devicetree/bindings/display/panel/samsung,atna33xc20.yaml
> > @@ -14,7 +14,11 @@ allOf:
> >
> >  properties:
> >    compatible:
> > -    const: samsung,atna33xc20
> > +    enum:
> > +      # Samsung 13.3" FHD (1920x1080 pixels) eDP AMOLED panel
> > +      - samsung,atna33xc20
> > +      # Samsung 14.5" WQXGA+ (2880x1800 pixels) eDP AMOLED panel
> > +      - samsung,atna45af01
> 
> Seems OK, but a few thoughts:
> 
> 1. Is it worth renaming this file? Something like
> "samsung,atna-oled-panel.yaml"? I'd be interested in DT maintainer
> folks' opinions here.
> 

I think examples for both approaches exist in the kernel tree, so I am
also interested in the opinion of the DT maintainers here. :-)

> 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.

I don't mind changing it, if there is consensus that we should ignore
this and use the fallback compatible instead.

Thanks,
Stephan