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 18:14:51 +0000
From: Conor Dooley <conor@...nel.org>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
	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 Fri, Mar 22, 2024 at 12:26:10PM -0400, Sean Anderson wrote:
> 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:

I'd rather you just picked the oldest device and used that as the
fallback, rather than introducing an "<blah>-sfp-2.0" compatible.
The 2.1 and 3.0 ones don't have anything like that.

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

None of the seem to be documented either btw:
rg fsl,qoriq-sfp-1.0
arch/powerpc/boot/dts/fsl/p5020si-post.dtsi
371:		compatible = "fsl,p5020-sfp", "fsl,qoriq-sfp-1.0";

arch/powerpc/boot/dts/fsl/p2041si-post.dtsi
339:		compatible = "fsl,p2041-sfp", "fsl,qoriq-sfp-1.0";

arch/powerpc/boot/dts/fsl/p4080si-post.dtsi
386:		compatible = "fsl,p4080-sfp", "fsl,qoriq-sfp-1.0";

arch/powerpc/boot/dts/fsl/p3041si-post.dtsi
366:		compatible = "fsl,p3041-sfp", "fsl,qoriq-sfp-1.0";

arch/powerpc/boot/dts/fsl/p5040si-post.dtsi
331:		compatible = "fsl,p5040-sfp", "fsl,qoriq-sfp-1.0";

> 
> 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

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