linux-kernel - Re: [PATCH 11/13] dt-bindings: lpspi: Update maximum num-cs value

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Message-ID: <ca3f3ed8-2708-4d22-a804-c094b449dc2d@linaro.org>
Date: Mon, 18 Aug 2025 13:49:04 +0100
From: James Clark <james.clark@...aro.org>
To: Rob Herring <robh@...nel.org>
Cc: Frank Li <Frank.Li@....com>, 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>,
 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>,
 Larisa Grigore <larisa.grigore@....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 11/13] dt-bindings: lpspi: Update maximum num-cs value



On 14/08/2025 9:59 pm, Rob Herring wrote:
> On Thu, Aug 14, 2025 at 05:06:51PM +0100, James Clark wrote:
>> As mentioned in commit f46b06e62c86 ("spi: spi-fsl-lpspi: Read
>> chip-select amount from hardware for i.MX93"), some devices support up
>> to 3 chip selects so update the max value.
>>
>> This isn't a fix or functional change because the devices with 3 chip
>> selects support reading the number of chip selects from hardware, so the
>> value wouldn't have needed to be set here. However the commit states
>> that the DT could be used to overwrite any HW value, so the full range
>> should be supported. This also avoids confusion for any readers about
>> how many chip selects there are.
> 
> If reading the h/w gives you 3, when would the DT need to override that
> with 3? You only need an override for 2 or less.
> 

Maybe it should say "currently the devices with 3 chip selects". I 
suppose there could be one in the future that has 3 but can't probe it.

TBH the main reason I added it was because it was confusing to work out 
what the actual max was. This says 2 when in reality it's 3. I suppose 
documenting that it should be left blank if reading from the hardware is 
supported might improve it too.

>>
>> Signed-off-by: James Clark <james.clark@...aro.org>
>> ---
>>   Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml b/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> index a65a42ccaafe..ce7bd44ee17e 100644
>> --- a/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> +++ b/Documentation/devicetree/bindings/spi/spi-fsl-lpspi.yaml
>> @@ -64,7 +64,7 @@ properties:
>>       description:
>>         number of chip selects.
>>       minimum: 1
>> -    maximum: 2
>> +    maximum: 3
>>       default: 1
>>   
>>     power-domains:
>>
>> -- 
>> 2.34.1
>>