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

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Message-ID: <48bb62eb-8aa9-465c-9e77-c0b375df0c9f@linaro.org>
Date: Tue, 25 Mar 2025 14:23:09 +0100
From: Caleb Connolly <caleb.connolly@...aro.org>
To: Krzysztof Kozlowski <krzk@...nel.org>, David Heidelberg <david@...t.cz>
Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, "Jason A. Donenfeld" <Jason@...c4.com>,
 Matthias Schiffer <matthias.schiffer@...tq-group.com>,
 Vincent Huang <vincent.huang@...synaptics.com>, linux-input@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 phone-devel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v3 1/7] dt-bindings: input: syna,rmi4: document
 syna,pdt-fallback-desc

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@...aro.org>
>>>>
>>>> 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.

The third party chips were designed to work with a specific downstream 
driver which doesn't implement the self-describing features of RMI4 and 
just hardcoded the functionality they expect.

Kind regards,
> 
> Best regards,
> Krzysztof

-- 
Caleb (they/them)