[U-Boot] [PATCH v5] bitops: introduce BIT() definition

[Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>]

On 09.09.15 20:10, Scott Wood wrote:
> On Wed, 2015-09-09 at 12:37 -0400, Tom Rini wrote:
>> On Wed, Sep 09, 2015 at 11:22:25AM -0500, Scott Wood wrote:
>>> On Tue, 2015-09-08 at 21:01 +0300, ivan.khoronzhuk wrote:
>>>> Hi, Andreas
>>>>
>>>> On 07.09.15 14:43, Andreas Bie?mann wrote:
>>>>> From: Heiko Schocher <hs@denx.de>
>>>>>
>>>>> introduce BIT() definition, used in at91_udc gadget
>>>>> driver.
>>>>>
>>>>> Signed-off-by: Heiko Schocher <hs@denx.de>
>>>>> [remove all other occurrences of BIT(x) definition]
>>>>> Signed-off-by: Andreas Bie?mann <andreas.devel@googlemail.com>
>>>>> ---
>>>>> Full buildman is running
>>>>>
>>>>
>>>> ....
>>>>
>>>>>
>>>>> +#define BIT(nr)            (1UL << (nr))
>>>>
>>>> Why UL? Why not simply 1 << (nr)?
>>>
>>> That would give the wrong result for nr == 31 if used as a 64-bit number,
>>> and
>>> would produce undefined behavior for nr >= 32 (though even with 1UL that
>>> would be undefined on 32-bit builds).
>>>
>>>> What if I need set ULL bit on 32-bit system?
>>>> Thanks for explanation.
>>>
>>> Yes, ULL would be better.
>>
>> That would be BIT_ULL(nr) ?  I want to assume that there was some care
>> given upstream here.  It was about 2 years ago now the kernel added a
>> specific BIT_ULL and family in addition to BIT(nr) from back in 2007.
>
> A quick search didn't turn up much justification for keeping them separate
> (and it seems like using BIT where BIT_ULL is needed could be a source of
> difficult bugs), but sure, we don't want to encourage writing driver code
> that will break on Linux.
Better to keep same approach.

>
> -Scott
>

-- 
Regards,
Ivan Khoronzhuk