Re: [PATCH 6.12.y-cip 14/23] mfd: syscon: Allow syscon nodes without a "syscon" compatible

Hi!

> From: "Rob Herring (Arm)" <[email protected]>
> 
> [ Upstream commit ba5095ebbc7a83965ac049a50fa493d7c751f19b ]
> 
> of_syscon_register_regmap() was added for nodes which need a custom
> regmap setup. It's not really correct for those nodes to claim they are
> compatible with "syscon" as the default handling likely doesn't work in
> those cases. If device_node_get_regmap() happens to be called first,
> then of_syscon_register() will be called and an incorrect regmap will be
> created (barring some other error). That may lead to unknown results in
> the worst case. In the best case, of_syscon_register_regmap() will fail
> with -EEXIST. This problem remains unless these cases drop "syscon" (an
> ABI issue) or we exclude them using their specific compatible. ATM,
> there is only one user: "google,gs101-pmu"
> 
> There are also cases of adding "syscon" compatible to existing nodes
> after the fact in order to register the syscon. That presents a
> potential DT ABI problem. Instead, if there's a kernel change needing a
> syscon for a node, then it should be possible to allow the kernel to
> register a syscon without a DT change. That's only possible by using
> of_syscon_register_regmap() currently, but in the future we may want to
> support a match list for cases which don't need a custom regmap.
> 
> With this change, the lookup functions will succeed for any node
> registered by of_syscon_register_regmap() regardless of whether the node
> compatible contains "syscon".

I note this is change to generic code. I trust it has all dependencies
it needs and will not cause problems somewhere?

Thanks and best regards,
								Pavel

> +++ b/drivers/mfd/syscon.c
> @@ -176,9 +176,12 @@ static struct regmap *device_node_get_regmap(struct device_node *np,
>  			break;
>  		}
>  
> -	if (!syscon)
> -		syscon = of_syscon_register(np, check_res);
> -
> +	if (!syscon) {
> +		if (of_device_is_compatible(np, "syscon"))
> +			syscon = of_syscon_register(np, check_res);
> +		else
> +			syscon = ERR_PTR(-EINVAL);
> +	}
>  	mutex_unlock(&syscon_list_lock);
>  
>  	if (IS_ERR(syscon))
> @@ -243,9 +246,6 @@ EXPORT_SYMBOL_GPL(device_node_to_regmap);
>  
>  struct regmap *syscon_node_to_regmap(struct device_node *np)
>  {
> -	if (!of_device_is_compatible(np, "syscon"))
> -		return ERR_PTR(-EINVAL);
> -
>  	return device_node_get_regmap(np, true);
>  }
>  EXPORT_SYMBOL_GPL(syscon_node_to_regmap);

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