[U-Boot] [PATCH 1/5] mmc: uniphier-sd: Factor out register IO

[Masahiro Yamada]

Hi.


2017-08-07 17:30 GMT+09:00 Marek Vasut <marek.vasut at gmail.com>:
> On 08/07/2017 04:30 AM, Masahiro Yamada wrote:
>> Hi Marek,
>
> Hi Masahiro,
>
> This is gonna be a great discussion, let's wrestle about consts and ints :-)
>
>> 2017-08-06 4:23 GMT+09:00 Marek Vasut <marek.vasut at gmail.com>:
>>> On 08/03/2017 02:36 PM, Masahiro Yamada wrote:
>>>> Hi Marek,
>>>
>>> Hi,
>>>
>>> [...]
>>>
>>>>> +static u32 uniphier_sd_readl(struct uniphier_sd_priv *priv, const u32 reg)
>>>>
>>>> "const" is unneeded here.
>>>
>>> Why? The function should not modify reg , so it is const.
>>
>>
>> Because "const" is useless here.
>>
>> The "reg" is not a pointer, so it is obvious
>> that there is no impact to the callers.
>>
>>
>>
>> Moreover, whether "reg" is constant or not
>> depends on how you implement the function.
>>
>>
>> If you force "const" to the argument, the only choice for the implementation
>> will be as follows:
>>
>>
>>
>> static u32 uniphier_sd_readl(struct uniphier_sd_priv *priv, const u32 reg)
>> {
>>       if (priv->caps & UNIPHIER_SD_CAP_64BIT)
>>              return readl(priv->regbase + (reg << 1));
>>       else
>>              return readl(priv->regbase + reg);
>> }
>>
>>
>>
>> If you want to implement the function as follows, you need to drop "const".
>>
>> static u32 uniphier_sd_readl(struct uniphier_sd_priv *priv, u32 reg)
>> {
>>       if (priv->caps & UNIPHIER_SD_CAP_64BIT)
>>               reg <<= 1;
>>
>>       return readl(priv->regbase + reg);
>> }
>
> My argument would be that the const prevents you from accidentally
> modifying the $reg inside the function.


No.
The arguments of a functions are local variables.
No impact on the outside of the scope of the function.

If you accidentally modify a variable where it should not,
it is a bug.  Just fix it.




If you want to wrestle more, please do it in LKML
by adding around "const".

For example,

drivers/base/regmap/regmap.c:
int regmap_write(struct regmap *map, unsigned int reg, unsigned int val)

arch/arm/include/asm/io.h:
static inline void __raw_writel(u32 val, volatile void __iomem *addr)





-- 
Best Regards
Masahiro Yamada