[PATCH v8 15/24] ACPI: Add support for nargs_prop in acpi_fwnode_get_reference_args()

[Rafael J. Wysocki]

On Fri, Jul 4, 2025 at 9:07 AM Anup Patel <apatel at ventanamicro.com> wrote:
>
> From: Sunil V L <sunilvl at ventanamicro.com>
>
> Currently, ACPI does not support the use of a nargs_prop (e.g.,
> associated with a reference in fwnode_property_get_reference_args().
> Instead, ACPI expects the number of arguments (nargs) to be explicitly
> passed or known.
>
> This behavior diverges from Open Firmware (OF), which allows the use of
> a #*-cells property in the referenced node to determine the number of
> arguments. Since fwnode_property_get_reference_args() is a common
> interface used across both OF and ACPI firmware paradigms, it is
> desirable to have a unified calling convention that works seamlessly for
> both.
>
> Add the support for ACPI to parse a nargs_prop from the referenced
> fwnode, aligning its behavior with the OF backend. This allows drivers
> and subsystems using fwnode_property_get_reference_args() to work in a
> firmware-agnostic way without having to hardcode or special-case
> argument counts for ACPI.
>
> Signed-off-by: Sunil V L <sunilvl at ventanamicro.com>
> Signed-off-by: Anup Patel <apatel at ventanamicro.com>

LGTM now, so

Acked-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>

> ---
>  drivers/acpi/property.c | 29 +++++++++++++++++++++++++----
>  drivers/base/property.c |  2 +-
>  2 files changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index d4863746fb11..e92402deee77 100644
> --- a/drivers/acpi/property.c
> +++ b/drivers/acpi/property.c
> @@ -804,13 +804,35 @@ acpi_fwnode_get_named_child_node(const struct fwnode_handle *fwnode,
>         return NULL;
>  }
>
> +static unsigned int acpi_fwnode_get_args_count(struct fwnode_handle *fwnode,
> +                                              const char *nargs_prop)
> +{
> +       const struct acpi_device_data *data;
> +       const union acpi_object *obj;
> +       int ret;
> +
> +       data = acpi_device_data_of_node(fwnode);
> +       if (!data)
> +               return 0;
> +
> +       ret = acpi_data_get_property(data, nargs_prop, ACPI_TYPE_INTEGER, &obj);
> +       if (ret)
> +               return 0;
> +
> +       return obj->integer.value;
> +}
> +
>  static int acpi_get_ref_args(struct fwnode_reference_args *args,
>                              struct fwnode_handle *ref_fwnode,
> +                            const char *nargs_prop,
>                              const union acpi_object **element,
>                              const union acpi_object *end, size_t num_args)
>  {
>         u32 nargs = 0, i;
>
> +       if (nargs_prop)
> +               num_args = acpi_fwnode_get_args_count(ref_fwnode, nargs_prop);
> +
>         /*
>          * Assume the following integer elements are all args. Stop counting on
>          * the first reference (possibly represented as a string) or end of the
> @@ -961,10 +983,10 @@ static int acpi_fwnode_get_reference_args(const struct fwnode_handle *fwnode,
>                                 return -EINVAL;
>
>                         element++;
> -
>                         ret = acpi_get_ref_args(idx == index ? args : NULL,
>                                                 acpi_fwnode_handle(device),
> -                                               &element, end, args_count);
> +                                               nargs_prop, &element, end,
> +                                               args_count);
>                         if (ret < 0)
>                                 return ret;
>
> @@ -979,9 +1001,8 @@ static int acpi_fwnode_get_reference_args(const struct fwnode_handle *fwnode,
>                                 return -EINVAL;
>
>                         element++;
> -
>                         ret = acpi_get_ref_args(idx == index ? args : NULL,
> -                                               ref_fwnode, &element, end,
> +                                               ref_fwnode, nargs_prop, &element, end,
>                                                 args_count);
>                         if (ret < 0)
>                                 return ret;
> diff --git a/drivers/base/property.c b/drivers/base/property.c
> index f626d5bbe806..6a63860579dd 100644
> --- a/drivers/base/property.c
> +++ b/drivers/base/property.c
> @@ -578,7 +578,7 @@ EXPORT_SYMBOL_GPL(fwnode_property_match_property_string);
>   * @prop:      The name of the property
>   * @nargs_prop:        The name of the property telling the number of
>   *             arguments in the referred node. NULL if @nargs is known,
> - *             otherwise @nargs is ignored. Only relevant on OF.
> + *             otherwise @nargs is ignored.
>   * @nargs:     Number of arguments. Ignored if @nargs_prop is non-NULL.
>   * @index:     Index of the reference, from zero onwards.
>   * @args:      Result structure with reference and integer arguments.
> --
> 2.43.0
>