Subject: Re: [PATCH 1/8] of: base: add of_parse_phandle_with_optional_args()

From: Rob Herring <[email-masked]>
Date: Mon, 10 Jan 2022 13:06:39 -0600

On Tue, Dec 28, 2021 at 03:25:42PM +0100, Michael Walle wrote:
> Add a new variant of the of_parse_phandle_with_args() which treats the
> cells name as optional. If it's missing, it is assumed that the phandle
> has no arguments.
> 
> Up until now, a nvmem node didn't have any arguments, so all the device
> trees haven't any '#*-cells' property. But there is a need for an
> additional argument for the phandle, for which we need a '#*-cells'
> property. Therefore, we need to support nvmem nodes with and without
> this property.
> 
> Signed-off-by: Michael Walle <[email-masked]>
> ---
>  drivers/of/base.c  | 23 +++++++++++++++++++++++
>  include/linux/of.h | 12 ++++++++++++
>  2 files changed, 35 insertions(+)
> 
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 5b907600f5b0..fb28bb26276e 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1543,6 +1543,29 @@ int of_parse_phandle_with_args(const struct device_node *np, const char *list_na
>  }
>  EXPORT_SYMBOL(of_parse_phandle_with_args);
>  
> +/**
> + * of_parse_phandle_with_optional_args() - Find a node pointed by phandle in a list
> + *
> + * Same as of_parse_phandle_args() except that if the cells_name property is
> + * not found, cell_count of 0 is assumed.
> + *
> + * This is used to useful, if you have a phandle which didn't have arguments
> + * before and thus doesn't have a '#*-cells' property but is now migrated to
> + * having arguments while retaining backwards compatibility.
> + */
> +int of_parse_phandle_with_optional_args(const struct device_node *np,
> +					const char *list_name,
> +					const char *cells_name, int index,
> +					struct of_phandle_args *out_args)
> +{
> +	if (index < 0)
> +		return -EINVAL;

I'm not sure why we didn't do this from the start, but just make index 
unsigned and then this check is not needed.

> +
> +	return __of_parse_phandle_with_args(np, list_name, cells_name,
> +					    0, index, out_args);
> +}
> +EXPORT_SYMBOL(of_parse_phandle_with_optional_args);

With the above, just make this static inline. Bonus points if you want 
to do the same changes on the other variants.

Rob