From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 16 Jul 2014 21:05:21 +0000 (+0000)
Subject: seqcount: Add raw_write_seqcount_latch()
X-Git-Tag: omap-for-v3.17/fixes-against-rc2~152^2~7
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9b0fd802e8c0545148324916055e7b40d97963fa;p=pandora-kernel.git

seqcount: Add raw_write_seqcount_latch()

For NMI safe access to clock monotonic we use the seqcount LSB as
index of a timekeeper array. The update sequence looks like this:

      smp_wmb();      <- prior stores to a[1]
      seq++;
      smp_wmb();      <- seq increment before update of a[0]
      update(a[0]);
      smp_wmb();      <- update of a[0]
      seq++;
      smp_wmb();      <- seq increment before update of a[1]
      update(a[1]);

To avoid open coded barriers, provide a helper function.

[ tglx: Split out of a combo patch against the first implementation of
  	the NMI safe accessor ]

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---

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