[U-Boot] [PATCH v4 3/4]: Define ffs/fls for all architectures

[Stefan Roese <sr@denx.de>]

Hi Simon,

On Tuesday 15 September 2009 22:34:43 Wolfgang Denk wrote:
> Dear Simon Kagstrom,
> 
> In message <20090824091012.0df5bbff@marrow.netinsight.se> you wrote:
> > Define ffs/fls for all architectures
> >
> > UBIFS requires fls(), which is not defined for arm (and some other
> > architectures) and this patch adds it. The implementation is taken from
> > Linux and is generic. ffs() is also defined for those that miss it.
> >
> > Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
> > ---
> > ChangeLog:
> >     v2: Unify code style (empty line between ffs/fls)
> >     v3: Move the definition to generic code (Mike Frysinger)
> >
> >  include/asm-i386/bitops.h  |    1 +
> >  include/asm-m68k/bitops.h  |    1 +
> >  include/asm-nios/bitops.h  |    1 +
> >  include/asm-nios2/bitops.h |    1 +
> >  include/asm-ppc/bitops.h   |    2 +
> >  include/asm-sh/bitops.h    |    2 +
> >  include/linux/bitops.h     |   45
> > ++++++++++++++++++++++++++++++++++++++++++++ 7 files changed, 53
> > insertions(+), 0 deletions(-)
> 
> Applied, thanks.

I'm seeing strange problem on some PPC4xx platforms (CFI FLASH driver on 
Sequoia) with recent U-Boot. Bisecting lead me to this patch. And looking at 
the PPC implementation, I can see that this can't work:

include/asm-ppc/bitops.h:
@@ -230,6 +231,7 @@ extern __inline__ int ffs(int x)
 {
 	return __ilog2(x & -x) + 1;
 }
+#define ffs

So after "ffs()" is define as an inline function, you define it to nothing. I 
understand that you need a flag for include/linux/bitops.h, to decide if the 
platform version of this function should be used or the generic version:

include/linux/bitops.h:
+#ifndef ffs
+# define ffs generic_ffs
+#endif

But this only works for platforms which don't supply a platform specific ffs 
function. One way to solve this would be something like this:

include/asm-ppc/bitops.h:
@@ -230,6 +231,7 @@ extern __inline__ int ffs(int x)
 {
 	return __ilog2(x & -x) + 1;
 }
+#define PLATFORM_FFS

include/linux/bitops.h:
+#ifndef PLATFORM_FFS
+# define ffs generic_ffs
+#endif


Perhaps there is an more elegant way to solve this problem. Patches welcome ;)

Thanks.

Cheers,
Stefan

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