linux-kernel - Re: [RFC] dt-bindings: firmware: scmi: Introduce compatible string

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Message-ID: <20250226160945.GA2505223-robh@kernel.org>
Date: Wed, 26 Feb 2025 10:09:45 -0600
From: Rob Herring <robh@...nel.org>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>
Cc: sudeep.holla@....com, cristian.marussi@....com, saravanak@...gle.com,
	krzk+dt@...nel.org, conor+dt@...nel.org, arm-scmi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, Peng Fan <peng.fan@....com>
Subject: Re: [RFC] dt-bindings: firmware: scmi: Introduce compatible string

On Wed, Feb 26, 2025 at 05:44:56PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@....com>
> 
> Add compatible string for the protocols by adding new nodes
> The current nodename pattern is "protocol@[0-9a-f]+$", the new node
> name will be "scmi-[a-z\-]+$".
> With compatible string and new nodename, cpufreq and devfreq could be
> separated into two nodes. And fwdevlink could correctly link suppliers
> and consumers.
> With compatible string, and driver updated.
> - Differnet vendor drivers with same SCMI protocol ID could be built in
>   without concerning vendor A's driver got probed when using vendor B's
>   SoC
> - NXP scmi pinctrl and ARM scmi pinctrl could be both built in, without
>   concerning arm scmi platform takes nxp scmi pinctrl node as supplier.

How are you going to handle DTs which aren't updated and still don't 
have compatible strings? Seems like that would be messy if not 
impossible.

> 
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
> 
> RFC:
>  This may sounds like that adding compatible to resovle linux driver issue.
>  Yes indeed. current scmi framework limitation makes it not work well with
>  fwdevlink, wrong suppliers maybe linked to consumers.
>  I have tried various's method to not introduce compatible, but rejected by
>  fwdevlink maintainer or scmi maintainer
>  There was a long discussion in [1][2][3].
>  [1] https://lore.kernel.org/arm-scmi/20240729070325.2065286-1-peng.fan@oss.nxp.com/
>  [2] https://lore.kernel.org/arm-scmi/20241225-scmi-fwdevlink-v1-0-e9a3a5341362@nxp.com/T/#mdd17c4b9b11af9fae0d5b6ec2e13756c2c6f977d
>  [3] https://lore.kernel.org/arm-scmi/20250120-scmi-fwdevlink-v2-0-3af2fa37dbac@nxp.com/
> 
>  The binding changes are posted out to see whether DT maintainer's view on
>  whether introduce compatible string is welcomed or not.
>  I not include driver changes, because this is just to see whether people
>  are happy with this or not.
> 
> Quote Sudeep's reply"
> I am not blocking you. What I mentioned is I don't agree that DT can be used
> to resolve this issue, but I don't have time or alternate solution ATM. So
> if you propose DT based solution and the maintainers agree for the proposed
> bindings I will take a look and help you to make that work. But I will raise
> any objections I may have if the proposal has issues mainly around the
> compatibility and ease of maintenance.
> "

This all looks to me like SCMI has failed to provide common interfaces.

I'm indifferent. If everyone involved thinks adding compatibles will 
solve whatever the issues are, then it's going to be fine with me 
(other than the issue above). It doesn't seem like you have that, so I 
don't know that I'd keep going down this path.

Rob