Re: [PATCH v2 2/3] iio: adc: aspeed: Use syscon phandle for trimming data when available

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Thu, Oct 01, 2026 at 05:50:37PM +0800, Billy Tsai wrote:
> aspeed_adc_set_trim_data() locates the SCU holding the ADC's
> reference-voltage trimming data with of_find_node_by_name(NULL,
> "syscon"), a global search that matches the first device-tree node
> named "syscon" regardless of which SCU instance it actually is.
> 
> On AST2700, which splits its SCU into "syscon0" (soc0) and "syscon1"
> (soc1), both nodes share the same node name "syscon" and only differ
> by label and unit address, so the lookup always resolves to syscon0
> even though the ADC's trimming data lives in syscon1.
> 
> Use the new "aspeed,trim-syscon" phandle property when present to look
> up the correct regmap directly, falling back to the old global by-name
> search when the property is absent so existing device trees keep
> working.

...

> -	syscon = of_find_node_by_name(NULL, "syscon");
> -	if (syscon == NULL) {
> -		dev_warn(data->dev, "Couldn't find syscon node\n");
> -		return -EOPNOTSUPP;
> +	scu = syscon_regmap_lookup_by_phandle_optional(data->dev->of_node, "aspeed,trim-syscon");

Do not dereference of_node, use dev_of_node(), it will help in the future
if we want to reorganise firmware nodes in the struct device.

> +	if (!scu) {
> +		/*
> +		 * No "aspeed,trim-syscon" phandle: either a single-SCU SoC, or a DTB
> +		 * predating the property. Fall back to the old global
> +		 * by-name lookup for backward compatibility.
> +		 */

So, why not doing

	struct device_node *np;
	const char *propname;
	...
	np = dev_of_node(data->dev);
	propname = "aspeed,trim-syscon";
	if (of_property_present(np, propname)) {
		scu = syscon_regmap_lookup_by_phandle(np, propname);
		...
	}
	...

?

> +		syscon = of_find_node_by_name(NULL, "syscon");
> +		if (syscon == NULL) {
> +			dev_warn(data->dev, "Couldn't find syscon node\n");
> +			return -EOPNOTSUPP;
> +		}
> +		scu = syscon_node_to_regmap(syscon);
> +		of_node_put(syscon);
>  	}
> -	scu = syscon_node_to_regmap(syscon);
> -	of_node_put(syscon);
>  	if (IS_ERR(scu)) {
>  		dev_warn(data->dev, "Failed to get syscon regmap\n");
>  		return -EOPNOTSUPP;

-- 
With Best Regards,
Andy Shevchenko