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Date: Wed, 14 May 2014 19:22:38 -0700 From: Brian Norris <computersforpeace@...il.com> To: Linux Kernel <linux-kernel@...r.kernel.org> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, linuxppc-dev@...ts.ozlabs.org, Andrew Morton <akpm@...ux-foundation.org>, David Howells <dhowells@...hat.com>, Brian Norris <computersforpeace@...il.com> Subject: roundup_pow_of_two() may not handle 64-bit integers Hi, I'm looking to use roundup_pow_of_two() (actually, order_base_2()) from <linux/log2.h>, but it seems that it only supports 64-bit integers if your toolchain uses a 64-bit 'unsigned long' type. This is strange, considering that ilog2() is explicitly designed for 32-bit or 64-bit compatibility. I also note that there is at least one location in which this limitation currently might be problematic: in pnv_pci_ioda2_set_bypass() (arch/powerpc/platforms/powernv/pci-ioda.c). It looks like this could be a problem if using large amounts of DRAM on a 32-bit PPC build, with 64-bit physical addresses. (There may be other cases like this one, but I haven't closely studied all callers of roundup_pow_of_two().) I'm thinking of cooking a patch to improve roundup_pow_of_two() (and thus order_base_2()), but I'd like to solicit comments on the basic problem first. Regards, Brian P.S. And of course, rounddown_pow_of_two() has the same issue. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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