Re: [PATCH 1/7] of: base: Add of_count_phandle_with_fixed_args()

[Robin Murphy <robin.murphy@arm.com>]

On 2020-10-14 19:39, Rob Herring wrote:
> On Wed, Oct 14, 2020 at 9:54 AM Richard Fitzgerald
> <rf@opensource.cirrus.com> wrote:
>>
>> Add an equivalent of of_count_phandle_with_args() for fixed argument
>> sets, to pair with of_parse_phandle_with_fixed_args().
>>
>> Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
>> ---
>>   drivers/of/base.c  | 42 ++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/of.h |  9 +++++++++
>>   2 files changed, 51 insertions(+)
>>
>> diff --git a/drivers/of/base.c b/drivers/of/base.c
>> index ea44fea99813..45d8b0e65345 100644
>> --- a/drivers/of/base.c
>> +++ b/drivers/of/base.c
>> @@ -1772,6 +1772,48 @@ int of_count_phandle_with_args(const struct device_node *np, const char *list_na
>>   }
>>   EXPORT_SYMBOL(of_count_phandle_with_args);
>>
>> +/**
>> + * of_count_phandle_with_fixed_args() - Find the number of phandles references in a property
>> + * @np:                pointer to a device tree node containing a list
>> + * @list_name: property name that contains a list
>> + * @cell_count: number of argument cells following the phandle
>> + *
>> + * Returns the number of phandle + argument tuples within a property. It
>> + * is a typical pattern to encode a list of phandle and variable
>> + * arguments into a single property.
>> + */
>> +int of_count_phandle_with_fixed_args(const struct device_node *np,
>> +                                    const char *list_name,
>> +                                    int cells_count)
>> +{
> 
> Looks to me like you can refactor of_count_phandle_with_args to handle
> both case and then make this and of_count_phandle_with_args simple
> wrapper functions.

Although for just counting the number of phandles each with n arguments 
that a property contains, isn't that simply a case of dividing the 
property length by n + 1? The phandles themselves will be validated by 
any subsequent of_parse_phandle*() call anyway, so there doesn't seem 
much point in doing more work then necessary here.

>> +       struct of_phandle_iterator it;
>> +       int rc, cur_index = 0;
>> +
>> +       if (!cells_count) {
>> +               const __be32 *list;
>> +               int size;
>> +
>> +               list = of_get_property(np, list_name, &size);
>> +               if (!list)
>> +                       return -ENOENT;
>> +
>> +               return size / sizeof(*list);

Case in point - if it's OK to do exactly that for n == 0, then clearly 
we're *aren't* fussed about validating anything, so the n > 0 code below 
is nothing more than a massively expensive way to check for a nonzero 
remainder :/

Robin.

>> +       }
>> +
>> +       rc = of_phandle_iterator_init(&it, np, list_name, NULL, cells_count);
>> +       if (rc)
>> +               return rc;
>> +
>> +       while ((rc = of_phandle_iterator_next(&it)) == 0)
>> +               cur_index += 1;
>> +
>> +       if (rc != -ENOENT)
>> +               return rc;
>> +
>> +       return cur_index;
>> +}
>> +EXPORT_SYMBOL(of_count_phandle_with_fixed_args);
>> +
>>   /**
>>    * __of_add_property - Add a property to a node without lock operations
>>    */
>> diff --git a/include/linux/of.h b/include/linux/of.h
>> index 5cf7ae0465d1..9f315da4e9da 100644
>> --- a/include/linux/of.h
>> +++ b/include/linux/of.h
>> @@ -377,6 +377,8 @@ extern int of_parse_phandle_with_fixed_args(const struct device_node *np,
>>          struct of_phandle_args *out_args);
>>   extern int of_count_phandle_with_args(const struct device_node *np,
>>          const char *list_name, const char *cells_name);
>> +extern int of_count_phandle_with_fixed_args(const struct device_node *np,
>> +       const char *list_name, int cells_count);
>>
>>   /* phandle iterator functions */
>>   extern int of_phandle_iterator_init(struct of_phandle_iterator *it,
>> @@ -886,6 +888,13 @@ static inline int of_count_phandle_with_args(struct device_node *np,
>>          return -ENOSYS;
>>   }
>>
>> +static inline int of_count_phandle_with_fixed_args(const struct device_node *np,
>> +                                                  const char *list_name,
>> +                                                  int cells_count)
>> +{
>> +       return -ENOSYS;
>> +}
>> +
>>   static inline int of_phandle_iterator_init(struct of_phandle_iterator *it,
>>                                             const struct device_node *np,
>>                                             const char *list_name,
>> --
>> 2.20.1
>>
> 
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