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

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Message-ID: <56D07ED6.7030607@nvidia.com>
Date:	Fri, 26 Feb 2016 11:35:34 -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 11:28 AM, Rhyland Klein wrote:
> 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
> 

Did you not see warnings like this when you compiled the kernel? Did you
find a different approach than what I proposed above to deal with it?
I'd like to get this in soon so that when the max77620 drivers are all
in and using it, it should be functional.

-rhyland

-- 
nvpublic