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

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Message-ID: <5060c248-3160-4d52-81ec-8e06bbd246bf@linaro.org>
Date: Wed, 26 Mar 2025 11:26:06 +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 3/26/25 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@...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.
> 
> 
> 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.

> 
> Best regards,
> Krzysztof

-- 
Caleb (they/them)