On 2019-03-07 9:28 am, Arnd Bergmann wrote:
On Thu, Mar 7, 2019 at 10:17 AM Robin Murphy <robin.mur...@arm.com> wrote:
On 2019-03-07 8:52 am, Arnd Bergmann wrote:
-#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
+/* double shift to work around https://bugs.llvm.org/show_bug.cgi?id=38789 */
+#define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<((n)-1))<<1)-1)
I think that now makes DMA_BIT_MASK(0) undefined - that shouldn't matter
in most cases, but it could potentially happen at runtime where callers
use a non-constant argument. However, it also means we don't need to
special-case 64 any more (since that's there to avoid the same thing
anyway), so we could simply flip that to handle 0 instead.
Yes, good idea.
FWIW I'd be very tempted to fold in the second shift as "2ULL<<((n)-1)",
but that may not be to everyone's taste.
I like that. So shall we do this?
/*
* Shifting '2' instead of '1' because of
* https://bugs.llvm.org/show_bug.cgi?id=38789
*/
#define DMA_BIT_MASK(n) (((n) == 0) ? 0ULL : ((2ULL<<((n)-1)))-1)
Neat - it was too early in the morning for me to think of a succinct way
to comment it, but that's great. I suspect there may be a redundant set
of parentheses around the shift still, but other than that,
Reviewed-by: Robin Murphy <robin.mur...@arm.com>
Cheers,
Robin.
