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

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Message-ID: <3c5e12fc-eb91-46e8-a558-9896f0bdcab4@ixit.cz>
Date: Mon, 24 Mar 2025 19:00:43 +0100
From: David Heidelberg <david@...t.cz>
To: 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,
 Caleb Connolly <caleb.connolly@...aro.org>
Subject: Re: [PATCH v3 1/7] dt-bindings: input: syna,rmi4: document
 syna,pdt-fallback-desc

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.

Some of them can be detected at runtime which is what this patchset 
tries to do.

> 
>>
>> Signed-off-by: Caleb Connolly <caleb.connolly@...aro.org>
>> Signed-off-by: David Heidelberg <david@...t.cz>
>> ---
>>   Documentation/devicetree/bindings/input/syna,rmi4.yaml | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/input/syna,rmi4.yaml b/Documentation/devicetree/bindings/input/syna,rmi4.yaml
>> index b522c8d3ce0db719ff379f2fefbdca79e73d027c..a80ec0c052cb1b7278f0832dd18ebd3256bc0874 100644
>> --- a/Documentation/devicetree/bindings/input/syna,rmi4.yaml
>> +++ b/Documentation/devicetree/bindings/input/syna,rmi4.yaml
>> @@ -49,6 +49,24 @@ properties:
>>       description:
>>         Delay to wait after powering on the device.
>>   
>> +  syna,pdt-fallback-desc:
>> +    $ref: /schemas/types.yaml#/definitions/uint8-matrix
>> +    description:
>> +      This property provides fallback values for certain register fields that
>> +      are missing on devices using third-party replacement displays.
>> +      These unofficial displays contain touch controllers that claim RMI4
>> +      compliance but fail to populate the function_number and function_version
>> +      registers of their Page Descriptor Table (PDT) entries.
>> +
>> +      Since the number of required fallback entries depends on the number of
>> +      Page Descriptor Tables supported by a given device, this property
>> +      should be provided on a best-effort basis.
>> +
>> +    items:
> 
> min/maxItems here

There is no hardcoded limit how many of these items will be provided, 
should I put there some huge range as 1..1024?

Thank you
David

> 
>> +      items:
>> +        - description: The 5th byte of the PDT entry (function number)
>> +        - description: The 4th byte of the PDT entry (version value)
> 
> Best regards,
> Krzysztof
> 

-- 
David Heidelberg