linux-kernel - Re: [PATCH] mfd: Fix MACRO for commonly declared MFD cell attributes

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Message-ID: <56C742C4.4080308@nvidia.com>
Date:	Fri, 19 Feb 2016 11:28:52 -0500
From:	Rhyland Klein <rklein@...dia.com>
To:	Lee Jones <lee.jones@...aro.org>
CC:	<linux-kernel@...r.kernel.org>,
	Laxman Dewangan <ldewangan@...dia.com>
Subject: Re: [PATCH] mfd: Fix MACRO for commonly declared MFD cell attributes

On 2/19/2016 3:50 AM, Lee Jones wrote:
> On Thu, 18 Feb 2016, Rhyland Klein wrote:
> 
>> MFD_ARRAY_SIZE() would not accurately return 0 if the passed
>> parameter was NULL. Fix this so that num_resources will
>> accurately be 0 in the case that _res is NULL.
>>
>> cc: Lee Jones <lee.jones@...aro.org>
>> cc: Laxman Dewangan <ldewangan@...dia.com>
>> Signed-off-by: Rhyland Klein <rklein@...dia.com>
>> ---
>>  include/linux/mfd/core.h | 15 +++++++++------
>>  1 file changed, 9 insertions(+), 6 deletions(-)
>>
>> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
>> index 1a5a87f3cd38..62136ccff1df 100644
>> --- a/include/linux/mfd/core.h
>> +++ b/include/linux/mfd/core.h
>> @@ -18,11 +18,11 @@
>>  
>>  #define MFD_ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
>>  
>> -#define MFD_CELL_ALL(_name, _res, _pdata, _id, _compat, _match)		\
>> +#define MFD_CELL_ALL(_name, _nres, _res, _pdata, _id, _compat, _match)	\
>>  	{								\
>>  		.name = (_name),					\
>>  		.resources = (_res),					\
>> -		.num_resources = MFD_ARRAY_SIZE((_res)),		\
>> +		.num_resources = (_nres),				\
>>  		.platform_data = (_pdata),				\
>>  		.pdata_size = MFD_ARRAY_SIZE((_pdata)), 		\
>>  		.of_compatible = (_compat),				\
>> @@ -31,16 +31,19 @@
>>  	}
>>  
>>  #define OF_MFD_CELL(_name, _res, _pdata, _id, _compat)			\
>> -		MFD_CELL_ALL(_name, _res, _pdata, _id, _compat, NULL)	\
>> +		MFD_CELL_ALL(_name, MFD_ARRAY_SIZE((_res)), _res,	\
>> +			_pdata, _id, _compat, NULL)			\
> 
> I'm confused.  Why would it be any different just by changing the call
> site of MFD_ARRAY_SIZE?

It isn't different, but for MFD_CELL_NAME, it explicitly passes 0
instead of using MFD_ARRAY_SIZE, as its the only place that doesn't
expect to have resources.

> 
> And what about .platform_data?

This crashed for me (without the change) at :

mfd_add_device():
        for (r = 0; r < cell->num_resources; r++) {
                res[r].name = cell->resources[r].name;
                res[r].flags = cell->resources[r].flags;

where dereferencing cell->resources[0] when there are no resources. I
guess the platform_data could do the same, but I didn't run into it.

> 
> How about this change instead?
> 
> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
> index 1a5a87f..8440f42 100644
> --- a/include/linux/mfd/core.h
> +++ b/include/linux/mfd/core.h
> @@ -16,7 +16,7 @@
>  
>  #include <linux/platform_device.h>
>  
> -#define MFD_ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
> +#define MFD_ARRAY_SIZE(arr) (arr ? (sizeof(arr) / sizeof((arr)[0])) : 0)
>  
>  #define MFD_CELL_ALL(_name, _res, _pdata, _id, _compat, _match)                \
>         {                                                               \
> 
That was my first thought too. However, I see this when I try to compile
that:

In file included from drivers/mfd/max77620.c:18:0:
include/linux/mfd/core.h:19:34: warning: the address of ‘gpio_resources’
will always evaluate as ‘true’ [-Waddress]
 #define MFD_ARRAY_SIZE(arr) (arr ? (sizeof(arr) / sizeof((arr)[0])) : 0)

7 different times. This patch was the only way I seemed to be able to
WAR around compile time warnings.

-rhyland

-- 
nvpublic