linux-kernel - Re: [PATCH 1/2] device property: Add optional nargs_prop for get_reference

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Message-ID: <Z_TgP0epJ3cJzlUt@smile.fi.intel.com>
Date: Tue, 8 Apr 2025 11:37:19 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
	devicetree@...r.kernel.org,
	Sakari Ailus <sakari.ailus@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J . Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Daniel Scally <djrscally@...il.com>, linux-kernel@...r.kernel.org,
	Danilo Krummrich <dakr@...nel.org>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 1/2] device property: Add optional nargs_prop for
 get_reference_args

On Mon, Apr 07, 2025 at 06:37:13PM -0400, Sean Anderson wrote:
> get_reference_args does not permit falling back to nargs when nargs_prop
> is missing. This makes it difficult to support older devicetrees where
> nargs_prop may not be present. Add support for this by converting nargs
> to a signed value. Where before nargs was ignored if nargs_prop was
> passed, now nargs is only ignored if it is strictly negative. When it is
> positive, nargs represents the fallback cells to use if nargs_prop is
> absent.

And what is the case to support old DTs on most likely outdated hardware?

...

>  	ret = fwnode_call_int_op(fwnode, get_reference_args, prop, nargs_prop,
> -				 nargs, index, args);
> +				 nargs_prop ? -1 : nargs, index, args);

>  	return fwnode_call_int_op(fwnode->secondary, get_reference_args, prop, nargs_prop,
> -				  nargs, index, args);
> +				  nargs_prop ? -1 : nargs, index, args);

I don't understand why it's needed here. The nargs_prop is passed to the callee.

...

> -				 unsigned int nargs, unsigned int index,
> +				 int nargs, unsigned int index,

As per above.

...

>  		error = property_entry_read_int_array(ref->node->properties,
>  						      nargs_prop, sizeof(u32),
>  						      &nargs_prop_val, 1);
> -		if (error)

> +

Stray blank line.

> +		if (error == -EINVAL) {

Why do we need an explicit error code check? This is fragile. Just check the
parameter before calling the above.

> +			if (nargs < 0)
> +				return error;
> +		} else if (error) {
>  			return error;
> -
> -		nargs = nargs_prop_val;
> +		} else {
> +			nargs = nargs_prop_val;
> +		}

...

>  of_fwnode_get_reference_args(const struct fwnode_handle *fwnode,
>  			     const char *prop, const char *nargs_prop,
> -			     unsigned int nargs, unsigned int index,
> +			     int nargs, unsigned int index,
>  			     struct fwnode_reference_args *args)

Same comments as per above.

-- 
With Best Regards,
Andy Shevchenko