[U-Boot] RFC: getramsize() prototype and volatile qualifier

[Mike Frysinger]

On Thu, Apr 21, 2011 at 1:50 PM, Albert ARIBAUD wrote:
> Le 21/04/2011 19:02, Mike Frysinger a écrit :
>> On Thu, Apr 21, 2011 at 3:09 AM, Albert ARIBAUD wrote:
>>> Call it a detail, but I see that get_ram_size() calls sometime qualify
>>> their argument as volatile and sometimes not, and this makes checkpatch
>>> complain that volatiles are Bad(tm), which I would like to get fixed.
>>>
>>> The prototype for get_ram_size() in is
>>>
>>>        long    get_ram_size  (volatile long *, long);
>>>
>>> While I understand that the way get_ram_size() works, it needs to
>>> perform volatile *accesses* to addresses computed from its arguments, I
>>> don't see why it requires one of the arguments themselves to be volatile.
>>>
>>> Am I missing something here, particularly about some toolchain requiring
>>> the argument to be volatile? I see no reason it should, but better safe
>>> than sorry.
>>
>> the argument isnt volatile, the memory it points to is.  since
>> get_ram_size() itself doesnt dereference the argument (only goes
>> through a local "addr"), the volatile marking in the prototype could
>> be dropped, but personally i dont see the point.  the prototype doesnt
>> require callers to add volatile markings to their own code, and i
>> could see someone using "base" in the future after the volatile being
>> dropped and people not noticing right away.  the current code is safe
>> and causes no problems by itself, so i see no value in changing it.
>>
>> this sounds like useless "gotta be checkpatch clean" work by people
>> blindly following its output.
>
> Just because checkpatch complains about something does not mean that
> particular complaint is without merit. :)

like ive said many times, "checkpatch clean" is not a hard rule.
review the output to see when it makes sense.  the general "volatile
is bad" check is there because people often screw it up.  this is not
one of those cases ... we absolutely want volatile accesses.

> Yes, the code works as it is; but it'll work just as well if volatile is
> removed from the prototype and calls

uhh, there is no "volatile in calls".  there is no requirement that
the call sites also use volatile markings.

>, and that'll make the code simpler and more homogeneous overall

i think you missed a fairly important qualifier.  this is your
opinion, and one i dont share in this particular instance.

> plus it'll give checkpatch one less cause for complaint. We gain
> something there, if not a functional plus, an overal quality plus.

there is absolutely no quality difference

> As for people fiddling with get_ram_size() *body* and removing the volatile
> 'addr' and use the non-volatile 'base' directly, why would they?

i have no idea.  i leave the door open to things that i dont happen to
think of rather than assuming absolutes.

> They will plainly see that 'addr' is volatile and 'base' is not

this sort of blind assumption is dangerous.  things that are plain to
you doesnt mean it's plain to everyone, and people make mistakes all
the time.  keeping the volatile markings on base protects from that
sort of screw up.

> (all the more because removing the volatile' attribute from 'base' will
> require casting it to 'base+int' where it belongs)

i dont know what you're talking about here ... there is no need for
casting regardless of the volatile markings of base.  casting is need
to ignore warnings when casting "down" from volatile to non-volatile,
not the other way around.  which is not the case here.
-mike