Messages in this thread | | | Date | Sun, 22 Jan 2012 00:54:40 +0900 | Subject | Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq | From | Hitoshi Mitake <> |
| |
On Sat, Jan 21, 2012 at 17:28, Ingo Molnar <mingo@elte.hu> wrote: > > * Linus Torvalds <torvalds@linux-foundation.org> wrote: > >> On Thu, Jan 19, 2012 at 5:01 PM, Matthew Wilcox >> <matthew.r.wilcox@intel.com> wrote: >> > The only places that uses readq/writeq are in the initialisation >> > path. Since they're not performance critical, always use readl/writel. >> >> The arch rules are that i fthe architecture has readq/writeq, they >> will be #define'd (they may be inline functions, but there will be a >> >> #define readq readq >> >> to make it visible to the preprocessor as well). >> >> So if you don't need the atomicity guarantees of a "real" readq, you >> can do this instead: >> >> #ifndef readq >> static inline u64 readq(void __iomem *addr) >> { >> return readl(addr) | (((u64) readl(addr + 4)) << 32LL); >> } >> #endif >> >> and then use readq() as if it existed. >> >> And I do think we should expose this in some generic manner. Because >> we currently don't, we already have that pattern copied in quite a few >> drivers. >> >> Maybe <asm-generic/io-nonatomic.h> or something? Making it >> clear that its not atomic, but avoiding the silly duplication >> we do now.. >> >> This whole mess was introduced in commit dbee8a0affd5 ("x86: >> remove 32-bit versions of readq()/writeq()"), and it already >> talked about the problems but didn't help with the drivers >> that simply don't care. >> >> All the people in those threads were doing their >> self-satisfied "writeq is broken", without much acknowledging >> that 99% of users simply don't seem to care. >> >> "Occupy Writeq - We are the 99%" > > Agreed, and offering a generic facility for silly duplication > was the motivation of the original commit by Hitoshi Mitake. > > This: > > | The presense of a writeq() implementation on 32-bit x86 that > | splits the 64-bit write into two 32-bit writes turns out to > | break the mpt2sas driver (and in general is risky for drivers > | as was discussed in > | <http://lkml.kernel.org/r/adaab6c1h7c.fsf@cisco.com>). > > is actually a mostly bogus statement and creates more problems > than it solves. > > Hitoshi-san, would you be interested in re-adding the generic > readq/writeq definitions in a slight variation to 2c5643b1c5, to > a separate io-nonatomic.h file, so that drivers that want it can > #include that file and be happy?
It sounds nice. In the previous discussion, I suggested that chaning the name of non-atomic readq/writeq to readq_nonatomic/writeq_nonatomic. And James Bottomley replied that it is fine but not really very useful:
https://lkml.org/lkml/2011/5/19/13
The idea of providing non-atomic readq/writeq in the new file with the name which express non-atomicity clearly might be able to satisfy both of safety and usefulness.
It will reduce the duplication of the definition. In addition readq/writeq users don't have to type the long symbols with _nonatomic suffix and can know non-atomicity from the name of header file.
I'd like to hear opinions from James, Roland and folks who dislike non-atomic readq/writeq.
-- 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/
| |