* Question about memcpy_fromio prototype
@ 2004-12-14 19:58 Matthew Wilcox
2004-12-14 20:15 ` Linus Torvalds
0 siblings, 1 reply; 2+ messages in thread
From: Matthew Wilcox @ 2004-12-14 19:58 UTC (permalink / raw)
To: Linus Torvalds; +Cc: linux-kernel
Hi Linus. On x86 and ia64, memcpy_fromio is protoyped as:
static inline void memcpy_fromio(void *dst, volatile void __iomem *src, int count)
ALSA does this (except on x86 and sparc32, so you don't see it):
int copy_to_user_fromio(void __user *dst, const void __iomem *src, size_t count)
[...]
memcpy_fromio(buf, src, c);
which provokes a warning from gcc that we're discarding a qualifier (the
'const') from src. Is ALSA just wrong? Or is the 'volatile' wrong?
--
"Next the statesmen will invent cheap lies, putting the blame upon
the nation that is attacked, and every man will be glad of those
conscience-soothing falsities, and will diligently study them, and refuse
to examine any refutations of them; and thus he will by and by convince
himself that the war is just, and will thank God for the better sleep
he enjoys after this process of grotesque self-deception." -- Mark Twain
^ permalink raw reply [flat|nested] 2+ messages in thread
* Re: Question about memcpy_fromio prototype
2004-12-14 19:58 Question about memcpy_fromio prototype Matthew Wilcox
@ 2004-12-14 20:15 ` Linus Torvalds
0 siblings, 0 replies; 2+ messages in thread
From: Linus Torvalds @ 2004-12-14 20:15 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: linux-kernel
On Tue, 14 Dec 2004, Matthew Wilcox wrote:
>
> Hi Linus. On x86 and ia64, memcpy_fromio is protoyped as:
>
> static inline void memcpy_fromio(void *dst, volatile void __iomem *src, int count)
>
> ALSA does this (except on x86 and sparc32, so you don't see it):
>
> int copy_to_user_fromio(void __user *dst, const void __iomem *src, size_t count)
> [...]
> memcpy_fromio(buf, src, c);
>
> which provokes a warning from gcc that we're discarding a qualifier (the
> 'const') from src. Is ALSA just wrong? Or is the 'volatile' wrong?
Neither. The right thing for a read-only IO pointer is actually
const volatile void __iomem *
which looks funny ("const volatile"?) but makes sense for prototypes,
exactly because a "const volatile" pointer is the most permissive kind of
pointer there is. And it actually does describe the thing perfectly: it is
"const" because we don't write to it ("const" in C does not mean that the
thing is constant, and never has, confusing name and some C++ semantic
changes aside) and obviously as an IO area it's both "volatile" and
"__iomem".
On x86, readb/w/l already gets that right, so I'll just fix
memcpy_fromio(). Other architectures can sort out themselves (ppc64 is
already correct, at least for eeh).
Linus
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