linux-kernel - Re: [PATCH 1/2] dt-bindings: nvmem: Remove fsl,t1023-sfp in favor of fsl,layerscape-sfp

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Date: Fri, 22 Mar 2024 12:26:10 -0400
From: Sean Anderson <sean.anderson@...ux.dev>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 Conor Dooley <conor@...nel.org>
Cc: Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
 Richard Alpe <richard@...42.se>, linux-kernel@...r.kernel.org,
 Niklas Söderlund <niklas.soderlund@...natech.se>,
 Michael Walle <michael@...le.cc>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: nvmem: Remove fsl,t1023-sfp in favor of
 fsl,layerscape-sfp

On 3/22/24 03:01, Krzysztof Kozlowski wrote:
> On 21/03/2024 17:21, Sean Anderson wrote:
>> On 3/19/24 13:55, Conor Dooley wrote:
>>> On Mon, Mar 18, 2024 at 11:48:06AM -0400, Sean Anderson wrote:
>>>> On 3/18/24 11:40, Conor Dooley wrote:
>>>>> On Mon, Mar 18, 2024 at 11:08:00AM -0400, Sean Anderson wrote:
>>>>>> On 3/17/24 11:10, Conor Dooley wrote:
>>>>>
>>>>>>> Additionally, should
>>>>>>> they fall back to t1023-sfp? I see that there's already some dts files
>>>>>>> with these compatibles in them but seemingly no driver support as there
>>>>>>> is for the t1023-sfp.
>>>>>>
>>>>>> I checked the reference manuals for these processors, and all of them use TA 2.0.
>>>>>
>>>>> Sounds like a fallback is suitable then, although that will require
>>>>> updating the various dts files.
>>>>
>>>> Yes, a fallback (like what is done for the T-series) would be suitable,
>>>> but given that these devicetrees have been in-tree for eight years I
>>>> think it would be preferable to support the existing bindings for
>>>> compatibility purposes.
>>>
>>> Just cos stuff snuck into the tree in dts files doesn't make it right
>>> though, I'd rather the bindings were done correctly. I don't care if you
>>> want to support all of the compatibles in the driver so that it works
>>> with the existing devicetrees though, as long as you mention the
>>> rationale in the commit message.
>> 
>> It doesn't really matter what the schema has as long as the driver supports
>> existing device trees.
> 
> We do not talk about driver now but bindings. You add new compatibles on
> a basis that they were already used. This cannot bypass regular review
> comments, so if during regular review process we would require
> fallbacks, then you are expected to listen to review also when
> documenting existing compatibles. Otherwise everyone would prefer to
> snuck in incorrect code and later document it "it was there!".

To be clear, the existing nodes look like

	sfp: sfp@...00 {
		compatible = "fsl,t1040-sfp";
		reg	   = <0xe8000 0x1000>;
	};

which is perfectly serviceable for read-only use (as the clock is only
necessary for writing). As these devices are effectively identical, the
compatible could also look like what the P-series has:

	sfp: sfp@...00 {
		compatible = "fsl,p2041-sfp", "fsl,qoriq-sfp-1.0";
		reg	   = <0xe8000 0x1000>;
	};

but in either case, it is desirable for the driver to match based on the
more-specific compatible (as well as the less-specific compatible) as we
already have enough information from the more-specific compatible to
select the correct implementation.

--Sean