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

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Message-ID: <3f401e84-7236-457f-a2ce-ee45898f1ab9@linaro.org>
Date: Mon, 18 Aug 2025 14:31:50 +0100
From: James Clark <james.clark@...aro.org>
To: Frank Li <Frank.li@....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>,
 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 7:28 pm, Frank Li 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.
>>
>> 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
> 
> You need keep the same restriction for other compatible string, or need

Not sure I follow here. Don't the binding docs only cover the maximum 
range of valid inputs for all covered platforms? They don't go into 
details about which ranges are valid for every individual sub-platform.

For example if a platform didn't support DMA we wouldn't say it's not 
valid to label DMA channels in the binding doc. If someone puts 3 
instead of 2 then that's just a mistake, but documenting valid ranges 
can't really fix a mistake like that. And changing 2 to 3 doesn't break 
existing DTs, only making it smaller would.

> reason for other platform which also support up to 3.

The reason is that some platforms support 3, so I thought it made most 
sense to set the max to 3. I replied more on the thread with Rob, but we 
can just drop this one.

> 
> Frank
> 
>>       default: 1
>>
>>     power-domains:
>>
>> --
>> 2.34.1
>>