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

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Message-ID: <2d555c27-1cb1-4ea9-9327-e1a3774e103b@ixit.cz>
Date: Fri, 28 Mar 2025 23:45:37 +0100
From: David Heidelberg <david@...t.cz>
To: Caleb Connolly <caleb.connolly@...aro.org>,
 Krzysztof Kozlowski <krzk@...nel.org>
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 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@...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.

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