Messages in this thread | | | Date | Sun, 5 Feb 2012 00:34:42 +0900 | Subject | Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq | From | Hitoshi Mitake <> |
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On Thu, Feb 2, 2012 at 10:05, James Bottomley <jbottomley@parallels.com> wrote: > On Wed, 2012-02-01 at 15:35 -0800, Linus Torvalds wrote: >> On Tue, Jan 31, 2012 at 4:23 AM, Ingo Molnar <mingo@elte.hu> wrote: >> > >> > non-atomic sounds good to me too. >> >> You both apparently missed the related discussion that some devices >> really do care about order, even if they don't care about atomicity. >> >> So we'd actually have two versions of the header file, one >> little-endian, and one big-endian. Then the driver that knows it >> doesn't need the atomic 'readq()' that is always defined, but wants a >> low-bytes-first version would just do >> >> #include <linux/io64-little-endian.h> >> >> (or "big-endian" if it wants to read/write high bits first). Most >> drivers probably don't care, but apparently NVMe does. > > And this was about the point I concluded last time that it simply wasn't > worth it with the number of different possibilities for the primitives > and trying to come up with a sensible naming scheme ... it's just easier > to open code because then you get exactly what you meant. > > Incidentally, the last time this came up was with mpt fusion: for a > write to a 64 bit register, it didn't care about order, but it did care > about interleaving as in if you write one half of a 64 bit register and > then write to another register, the 64 bit register effectively gets > written with zeros in the part you didn't write to, so we had to put a > spin lock in the open coded writeb/w/l/q() to make sure the card didn't > get interleaved writes. > > James >
As you say, readq/writeq without any description about the semantics of atomicity will cause confusion in such a case.
But new plan for non-atomic readq/writeq is defining non-atomic readq/writeq in the header file like asm-generic/io-nonatomic-hi-lo.h, and the file name is a good documentation for the description.
The drivers which use readq/writeq without the line like #include <asm-generic/io-nonatomic-hi-lo.h> will cause compile error in the 32-bit environment.
-- Hitoshi Mitake h.mitake@gmail.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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