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

[Masahiro Yamada]

2017-08-17 15:39 GMT+09:00 Jaehoon Chung <jh80.chung at samsung.com>:
> On 08/13/2017 01:55 AM, Marek Vasut wrote:
>> On 08/10/2017 09:49 AM, Masahiro Yamada wrote:
>>> 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.
>
> Is there any case about modifying the regs value in this function?
> Well..I think that it makes sense about both. (Masahiro and Marek opinion)
>
> But There is nothing wrong to prevent from accidentally.


In my opinion, const is useful for pointer dereference,
but unneeded in this case.

I believe it is the taste
from what I saw from Linux code.  So, I follow it.



-- 
Best Regards
Masahiro Yamada