Re: [PATCH 1/4] of: Add of_parse_phandle_with_opt_args() helper function

[Rob Herring]

On Tue, Sep 22, 2015 at 12:52 PM, Marc Zyngier <marc.zyngier@xxxxxxx> wrote:
> of_parse_phandle_with_args() is slightly inflexible as it doesn't
> allow the (unusual) case where the #*-cells property is not defined.
> In order to support this, introduce of_parse_phandle_with_opt_args()
> which assumes that #*-cells is zero when it is not defined,

zero or cell_count - 1?

I would be okay with always assuming zero rather than being an error
if that simplifies things. It is not really the kernel's job to be a
dtb validator.

Also, I assume this was done for some compatibility? In general, we
should be explicit, so "#msi-cells = <0>" should be recommended and we
should update dts files if they are not.

Rob

> as required by the msi-parent binding
>
> This is done by turning __of_parse_phandle_with_args into an even
> bigger monster, which is a bit frightening.
>
> Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> ---
>  drivers/of/base.c  | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  include/linux/of.h |  3 +++
>  2 files changed, 65 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 8b5a187..1612342e 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -1479,6 +1479,10 @@ static int __of_parse_phandle_with_args(const struct device_node *np,
>                          * (i.e. cells_name not set, but cell_count is set),
>                          * except when we're going to return the found node
>                          * below.
> +                        *
> +                        * If #*-cells is not found, but cell_count is set
> +                        * to a non-zero value, use (cell_count-1) as a
> +                        * fallback value.
>                          */
>                         if (cells_name || cur_index == index) {
>                                 node = of_find_node_by_phandle(phandle);
> @@ -1490,13 +1494,21 @@ static int __of_parse_phandle_with_args(const struct device_node *np,
>                         }
>
>                         if (cells_name) {
> -                               if (of_property_read_u32(node, cells_name,
> -                                                        &count)) {
> +                               int ret;
> +                               ret = of_property_read_u32(node, cells_name,
> +                                                          &count);
> +                               if (ret && !cell_count) {
>                                         pr_err("%s: could not get %s for %s\n",
>                                                 np->full_name, cells_name,
>                                                 node->full_name);
>                                         goto err;
>                                 }
> +                               if (ret) {
> +                                       count = cell_count - 1;
> +                                       pr_debug("%s: could not get %s for %s, assuming %d\n",
> +                                                np->full_name, cells_name,
> +                                                node->full_name, count);
> +                               }
>                         } else {
>                                 count = cell_count;
>                         }
> @@ -1628,6 +1640,54 @@ 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_opt_args() - Find a node pointed by phandle in a list
> + * @np:                pointer to a device tree node containing a list
> + * @list_name: property name that contains a list
> + * @cells_name:        property name that specifies phandles' arguments count
> + * @index:     index of a phandle to parse out
> + * @out_args:  optional pointer to output arguments structure (will be filled)
> + *
> + * This function is useful to parse lists of phandles and their arguments.
> + * If cells_name is not found, then it is assumed to be zero.
> + * Returns 0 on success and fills out_args, on error returns appropriate
> + * errno value.
> + *
> + * Caller is responsible to call of_node_put() on the returned out_args->np
> + * pointer.
> + *
> + * Example:
> + *
> + * phandle1: node1 {
> + *     #list-cells = <2>;
> + * }
> + *
> + * phandle2: node2 {
> + * }
> + *
> + * phandle3: node3 {
> + *     #list-cells = <1>;
> + * }
> + *
> + * node3 {
> + *     list = <&phandle1 1 2 &phandle2 &phandle 3>;
> + * }
> + *
> + * To get a device_node of the `node2' node you may call this:
> + * of_parse_phandle_with_args(node3, "list", "#list-cells", 1, &args);
> + */
> +int of_parse_phandle_with_opt_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;
> +       return __of_parse_phandle_with_args(np, list_name, cells_name, 1,
> +                                           index, out_args);
> +}
> +EXPORT_SYMBOL(of_parse_phandle_with_opt_args);
> +
> +/**
>   * of_parse_phandle_with_fixed_args() - Find a node pointed by phandle in a list
>   * @np:                pointer to a device tree node containing a list
>   * @list_name: property name that contains a list
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 2194b8c..ae6cd03 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -328,6 +328,9 @@ extern struct device_node *of_parse_phandle(const struct device_node *np,
>  extern int of_parse_phandle_with_args(const struct device_node *np,
>         const char *list_name, const char *cells_name, int index,
>         struct of_phandle_args *out_args);
> +extern int of_parse_phandle_with_opt_args(const struct device_node *np,
> +       const char *list_name, const char *cells_name, int index,
> +       struct of_phandle_args *out_args);
>  extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
>         const char *list_name, int cells_count, int index,
>         struct of_phandle_args *out_args);
> --
> 2.1.4
>
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