From: Linus Torvalds <torvalds@linux-foundation.org>
To: Matthew Wilcox <matthew.r.wilcox@intel.com>,
Roland Dreier <roland@purestorage.com>,
Andrew Morton <akpm@linux-foundation.org>,
Hitoshi Mitake <h.mitake@gmail.com>,
James Bottomley <James.Bottomley@parallels.com>,
Ingo Molnar <mingo@elte.hu>
Cc: linux-kernel@vger.kernel.org, linux-nvme@infradead.org,
hpa@linux.intel.com
Subject: Re: [PATCH] NVMe: Fix compilation on architecturs without readq/writeq
Date: Thu, 19 Jan 2012 17:21:31 -0800 [thread overview]
Message-ID: <CA+55aFwmDbDm5+12Nc0wnu7J8dsOKW0tCd_tVf-3pwQOq9MF3w@mail.gmail.com> (raw)
In-Reply-To: <1327021265-22184-1-git-send-email-matthew.r.wilcox@intel.com>
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%"
Linus
next prev parent reply other threads:[~2012-01-20 1:21 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-01-20 1:01 [PATCH] NVMe: Fix compilation on architecturs without readq/writeq Matthew Wilcox
2012-01-20 1:21 ` Linus Torvalds [this message]
2012-01-20 17:43 ` Wilcox, Matthew R
2012-01-21 8:28 ` Ingo Molnar
2012-01-21 15:54 ` Hitoshi Mitake
2012-01-21 16:58 ` Ingo Molnar
2012-01-23 16:05 ` Hitoshi Mitake
2012-01-23 16:57 ` Linus Torvalds
2012-01-23 23:04 ` H. Peter Anvin
2012-01-29 8:02 ` Hitoshi Mitake
2012-01-31 3:03 ` Linus Torvalds
2012-01-31 3:05 ` Linus Torvalds
2012-02-04 15:25 ` Hitoshi Mitake
2012-01-31 11:58 ` Alan Cox
2012-01-31 12:09 ` Ingo Molnar
2012-01-31 12:18 ` Alan Cox
2012-01-31 12:23 ` Ingo Molnar
2012-02-01 23:35 ` Linus Torvalds
2012-02-02 1:05 ` James Bottomley
2012-02-02 1:15 ` Linus Torvalds
2012-02-02 15:05 ` H. Peter Anvin
2012-02-04 15:39 ` Hitoshi Mitake
2012-02-05 6:53 ` Geert Uytterhoeven
2012-02-05 7:01 ` Hitoshi Mitake
2012-02-04 15:34 ` Hitoshi Mitake
2012-02-07 2:48 ` Hitoshi Mitake
2012-02-04 15:24 ` Hitoshi Mitake
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