Messages in this thread | | | Date | Tue, 29 Mar 2011 18:02:11 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH 05/30] amd64_edac: Cleanup chipselect handling |
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On Tue, Mar 29, 2011 at 11:39:09AM -0400, Mauro Carvalho Chehab wrote: > >>> + * Create a contiguous bitmask starting at bit position @lo and ending at > >>> + * position @hi. For example > >>> + * > >>> + * GENMASK(21, 39) gives us the 64bit vector 0x000000ffffe00000. > >>> + */ > >>> +#define GENMASK(lo, hi) (((1ULL << ((hi) - (lo) + 1)) - 1) << (lo)) > >>> + > >> > >> This is a nice macro that could be useful outside amd64. It is probably a good > >> idea to move it to include/linux/bitops.h. > > > > I'd suggest rather <drivers/edac/edac_core.h> if you want to use it in > > EDAC. But if we have more users, I don't have a problem with putting > > it there (or somewhere else generic enough if people have a better > > suggestion). > > Yeah, other edac drivers could benefit of using it, and also could benefit on a > variant that would do an AND operation and shift it, something like (untested): > > /* > * Create a contiguous bitmask starting at bit position @lo and ending at > * position @hi. For example > * > * APPLY_BITMASK(v, 21, 39) will return the result of: > * (v & 0x000000ffffe00000) >> 21 > */ > #define APPLY_BITMASK(v, lo, hi) (((v) & ((1ULL << ((hi) - (lo) + 1)) - 1) << (lo)) >> (lo))
The macro definition doesn't match the comment. In the comment you do a bitwise AND first and shift the result then. The way you've written it, it does
((v & 0x000000000007ffff << 21) >> 21)
you need to fixup the brackets:
#define APPLY_BITMASK(v, lo, hi) (((v) & (((1ULL << ((hi) - (lo) + 1)) - 1) << (lo))) >> (lo))
Also, this doesn't only apply it but shifts too, so it should be
#define APPLY_BITMASK_AND_SHIFT(...)
But this macro gets too special to put it in shared code.
> Almost all edac drivers do something like the above, for example, to get DIMM rows/cols/banks, etc. > > Probably, the most complex part is to find a nice name for it ;) > > Yet, I think non-edac drivers could also benefit of such macro, and, as this is not > edac-specific, I think it would be better to add it at bitops.h.
No, this should go into generic code only if it has users - "it might benefit" is not strong-enough an argument for polluting generic code. I'd leave it in edac_core.h and push it somewhere more generic only when I need it in other subsystems.
-- Regards/Gruss, Boris.
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