Re: [PATCH] of: Drop redundant check in linker section OF match table

[Mukesh Ojha]

On 3/21/2019 1:25 AM, Frank Rowand wrote:
> On 3/20/19 3:49 AM, Mukesh Ojha wrote:
> > Existing check of `fn` against NULL inside OF match table
> > is redundant. Remove the check.
> >
> > Signed-off-by: Mukesh Ojha <mojha@xxxxxxxxxxxxxx>
> > Cc: Rob Herring <robh@xxxxxxxxxx>
> > Cc: Frank Rowand <frowand.list@xxxxxxxxx>
> > Cc: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
> > Cc: devicetree@xxxxxxxxxxxxxxx
> > ---
> >   include/linux/of.h | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index e240992..b86c00a 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -1283,13 +1283,13 @@ static inline int of_get_available_child_count(const struct device_node *np)
> >   	static const struct of_device_id __of_table_##name		\
> >   		__used __section(__##table##_of_table)			\
> >   		 = { .compatible = compat,				\
> > -		     .data = (fn == (fn_type)NULL) ? fn : fn  }
> > +		     .data = fn }
> >   #else
> >   #define _OF_DECLARE(table, name, compat, fn, fn_type)			\
> >   	static const struct of_device_id __of_table_##name		\
> >   		__attribute__((unused))					\
> >   		 = { .compatible = compat,				\
> > -		     .data = (fn == (fn_type)NULL) ? fn : fn }
> > +		     .data = fn }
> >   #endif
> >   
> >   typedef int (*of_init_fn_2)(struct device_node *, struct device_node *);
> The check is not redundant and does serve a purpose.
>
> The purpose is not very obvious on the surface, but it is checking that
> the function fn() is of the proper type.

Frank,

Thanks for taking out time to explain the stuff, Yeah some miscellaneous 
driver can do this type of mistake.

-Mukesh


> An example of a compiler warning with a bad function type is created
> by applying the following patch:
>
>     drivers/of/unittest.c:62:1: warning: comparison of distinct pointer types lacks a cast [enabled by default]
>
> Note that you need to have CONFIG_UNITTEST enabled to compile unittest.c.
>
> Line 62 is
>     OF_DECLARE_1(__unittest_of_table, unittest_setup_2_bad, "unittest_compat",
>
> ---
>   drivers/of/unittest.c |   17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
>
> Index: b/drivers/of/unittest.c
> ===================================================================
> --- a/drivers/of/unittest.c
> +++ b/drivers/of/unittest.c
> @@ -45,6 +45,23 @@ static struct unittest_results {
>   	failed; \
>   })
>   
> +struct of_device_id __unittest_of_table;
> +
> +static void __init unittest_setup_1_good(struct device_node *np)
> +{
> +}
> +
> +static void __init unittest_setup_2_bad(struct device_node *np_1,
> +	struct device_node *np_2)
> +{
> +}
> +
> +OF_DECLARE_1(__unittest_of_table, unittest_setup_1_good, "unittest_compat",
> +	unittest_setup_1_good);
> +
> +OF_DECLARE_1(__unittest_of_table, unittest_setup_2_bad, "unittest_compat",
> +	unittest_setup_2_bad);
> +
>   static void __init of_unittest_find_node_by_name(void)
>   {
>   	struct device_node *np;