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Subject: Re: [PATCH] of: Drop redundant check in linker section OF match table
To:     Frank Rowand <frowand.list@gmail.com>, linux-kernel@vger.kernel.org
Cc:     Rob Herring <robh@kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        devicetree@vger.kernel.org
References: <1553078940-9907-1-git-send-email-mojha@codeaurora.org>
 <67db2d00-26d0-f9e3-f4dd-0f48633142a9@gmail.com>
From:   Mukesh Ojha <mojha@codeaurora.org>
Message-ID: <44f8ba04-8a50-fa81-8784-aaffc4f7c3cc@codeaurora.org>
Date:   Thu, 21 Mar 2019 13:09:29 +0530
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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@codeaurora.org>
>> Cc: Rob Herring <robh@kernel.org>
>> Cc: Frank Rowand <frowand.list@gmail.com>
>> Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
>> Cc: devicetree@vger.kernel.org
>> ---
>>   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;