[U-Boot] RFC: getramsize() prototype and volatile qualifier
Hi all,
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.
Amicalement,
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. -mike
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. -mike
Just because checkpatch complains about something does not mean that particular complaint is without merit. :)
Yes, the code works as it is; but it'll work just as well if volatile is removed from the prototype and calls, and that'll make the code simpler and more homogeneous overall, plus it'll give checkpatch one less cause for complaint. We gain something there, if not a functional plus, an overal quality plus.
As for people fiddling with get_ram_size() *body* and removing the volatile 'addr' and use the non-volatile 'base' directly, why would they? They will plainly see that 'addr' is volatile and 'base' is not (all the more because removing the volatile' attribute from 'base' will require casting it to 'base+int' where it belongs), and the very role of the function makes it clear to them that the volatile attribute is required for 'addr', so they'll keep 'addr'.
Plus, get_ram_size() is pretty stable -- actually, it has changed only once in 2006 since its creation in 2004.
Amicalement,
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
Le 22/04/2011 00:28, Mike Frysinger a écrit :
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.
Volatile accesses, yes, we want them, I said so. But that does not mean we need volatile *paramters* to the function or *arguments* to the calls.
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.
There *are* volatiles in the calls; just check the source code.
, 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.
Maybe you missed the fact that there are calls to get_ram_size() that don't have the volatile qualifier to 'base' and there are other who have it -- that's heterogeneity (I suspect it stems from various strictnesses in toolchains) and removing all volatiles objectively does remove that heterogeneity.
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
Less error / warning messages from a tool we use counts as better quality for me.
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.
I don't assume absolutes here I think. My assumtion is that 'people' will not blindly remove a volatile qualifier in a memory size test function which obviously requires its memory accesses to not be optimized in any way.
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.
If things are not plain, then let's make them plain where they need to be. We do agree that the qualifier in the prototype and calls is useless from a functional viewpoint; we do agree that the volatile *access* in the function body is crucial; if you think people who want to modify the body of get_ram_size() need an explicit warning about keeping the accesses volatile then that warning should be given right near the accesses, for instance in the form of a Big Fat Comment (tm) right in the function's code, not elsewhere in calls.
(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
Correct: the cast to volatile is not needed. Still, removing the 'base' variable will remove a 'volatile' qualifier. However, I still think people who want to modify get_ram_size() know about volatiles and how the function works and won't make the mistake of removing the qualifier. And if they do, the change will be reviewed and NAKed anyway.
Amicalement,
participants (2)
-
Albert ARIBAUD -
Mike Frysinger