Re: [PATCH v3 1/7] dt-bindings: input: syna,rmi4: document syna,pdt-fallback-desc

[David Heidelberg]

On 26/03/2025 11:26, Caleb Connolly wrote:
> On 3/26/25 07:57, Krzysztof Kozlowski wrote:
> > On 25/03/2025 14:23, Caleb Connolly wrote:
> > > On 3/25/25 08:36, Krzysztof Kozlowski wrote:
> > > > On 24/03/2025 19:00, David Heidelberg wrote:
> > > > > On 10/03/2025 10:45, Krzysztof Kozlowski wrote:
> > > > > > On Sat, Mar 08, 2025 at 03:08:37PM +0100, David Heidelberg wrote:
> > > > > > > From: Caleb Connolly <caleb.connolly@xxxxxxxxxx>
> > > > > > >
> > > > > > > This new property allows devices to specify some register values 
> > > > > > > which
> > > > > > > are missing on units with third party replacement displays. These
> > > > > > > displays use unofficial touch ICs which only implement a subset 
> > > > > > > of the
> > > > > > > RMI4 specification.
> > > > > >
> > > > > > These are different ICs, so they have their own compatibles. Why this
> > > > > > cannot be deduced from the compatible?
> > > > >
> > > > > Yes, but these identify as the originals.
> > > >
> > > >
> > > > It does not matter how they identify. You have the compatible for them.
> > > > If you cannot add compatible for them, how can you add dedicated
> > > > property for them?
> > >
> > > Hi Krzysztof,
> > >
> > > There are an unknown number of knock-off RMI4 chips which are sold in
> > > cheap replacement display panels from multiple vendors. We suspect
> > > there's more than one implementation.
> > >
> > > A new compatible string wouldn't help us, since we use the same DTB on
> > > fully original hardware as on hardware with replacement parts.
> > >
> > > The proposed new property describes configuration registers which are
> > > present on original RMI4 chips but missing on the third party ones, the
> > > contents of the registers is static.
> >
> >
> > So you want to add redundant information for existing compatible, while
> > claiming you cannot deduce it from that existing compatible... Well,
> > no.. you cannot be sure that only chosen boards will have touchscreens
> > replaced, thus you will have to add this property to every board using
> > this compatible making it equal to the compatible and we are back at my
> > original comment. This is deducible from the compatible. If not the new
> > one, then from old one.
>
> hmm I see, so instead we should add a compatible for the specific 
> variant (S3320 or something) of RMI4 in this device and handle this in 
> the driver? I think that makes sense.

Agree, preparing it for v4. So far proposing `compatible = 
"syna,rmi4-s3706b-i2c", "syna,rmi4-i2c"` (as S3706B is written in the 
commit and search confirms it for OP6/6T).

David>
> > Best regards,
> > Krzysztof

--
David Heidelberg