linux-kernel - Re: [PATCH 12/13] dt-bindings: lpspi: Document nxp,lpspi-pincfg property

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Message-ID: <bd59344b-9dc0-42bd-98c8-80ab9ca97123@linaro.org>
Date: Mon, 18 Aug 2025 15:47:45 +0100
From: James Clark <james.clark@...aro.org>
To: Frank Li <Frank.li@....com>, Larisa Grigore <larisa.grigore@....com>
Cc: Mark Brown <broonie@...nel.org>, Clark Wang <xiaoning.wang@....com>,
 Fugang Duan <B38611@...escale.com>, Gao Pan <pandy.gao@....com>,
 Fugang Duan <fugang.duan@....com>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
 Sascha Hauer <s.hauer@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
 Larisa Grigore <larisa.grigore@....nxp.com>,
 Ghennadi Procopciuc <ghennadi.procopciuc@....com>,
 Ciprianmarian Costea <ciprianmarian.costea@....com>, s32@....com,
 linux-spi@...r.kernel.org, imx@...ts.linux.dev,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 12/13] dt-bindings: lpspi: Document nxp,lpspi-pincfg
 property



On 14/08/2025 7:19 pm, Frank Li wrote:
> On Thu, Aug 14, 2025 at 05:06:52PM +0100, James Clark wrote:
>> Document the two valid pincfg values and the defaults.
>>
>> Although the hardware supports two more values for half-duplex modes,
>> the driver doesn't support them so don't document them.
> 
> binding doc should be first patch before drivers.
> 
> binding descript hardware not driver, you should add all regardless if
> driver support it.
> 

Replied to same on "[PATCH 10/13] spi: spi-fsl-lpspi: Add compatible for 
S32G"

>>
>> Signed-off-by: James Clark <james.clark@...aro.org>
>> ---
>>   Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml | 14 ++++++++++++++
>>   1 file changed, 14 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml b/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> index ce7bd44ee17e..3f8833911807 100644
>> --- a/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> +++ b/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> @@ -70,6 +70,19 @@ properties:
>>     power-domains:
>>       maxItems: 1
>>
>> +  nxp,pincfg:
>> +    description:
>> +      'Pin configuration value for CFGR1.PINCFG.
>> +        - "sin-in-sout-out": SIN is used for input data and SOUT is used for
>> +                             output data
>> +        - "sout-in-sin-out": SOUT is used for input data and SIN is used for
>> +                             output data
>> +      If no value is specified then the default is "sin-in-sout-out" for host
>> +      mode and "sout-in-sin-out" for target mode.'
> 
> why need this? are there varible at difference boards? look like default
> is more make sense.
> 

+ Larissa. I think this might also be a question for the hardware 
designers about why the feature to swap the pins was deemed worth including.

I'm assuming the flexibility is given for routing reasons. If you have 
another device with the pins in one order then you can route it without 
a via if they happen to be in the same order.

> SPI signal name is MOSI and MISO
> 
> Frank
> 

As mentioned in the commit message of "[PATCH 05/13] spi: spi-fsl-lpspi: 
Enumerate all pin configuration definitions" the names were taken 
directly from the reference manual and this doc text was too. I think 
diverging from CFGR1_PINCFG could be potentially quite confusing. And 
MOSI isn't mentioned once in S32G3RM rev 4:

   Configures which pins are used for input and output data during serial
   transfers. When performing parallel transfers, the Pin Configuration
   field is ignored.

     00b - SIN is used for input data and SOUT is used for output data
     01b - SIN is used for both input and output data, only half-duplex
           serial transfers are supported
     10b - SOUT is used for both input and output data, only half-duplex
           serial transfers are supported
     11b - SOUT is used for input data and SIN is used for output data

James

>> +    enum:
>> +      - sin-in-sout-out
>> +      - sout-in-sin-out
>> +
>>   required:
>>     - compatible
>>     - reg
>> @@ -95,4 +108,5 @@ examples:
>>           spi-slave;
>>           fsl,spi-only-use-cs1-sel;
>>           num-cs = <2>;
>> +        nxp,pincfg = "sout-in-sin-out";
>>       };
>>
>> --
>> 2.34.1
>>