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SubjectRE: [PATCH RESEND v8] iopoll: Introduce memory-mapped IO polling macros
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> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel-
> owner@vger.kernel.org] On Behalf Of Mitchel Humpherys
> Sent: Monday, 24 November, 2014 2:15 PM
...
> From: Matt Wagantall <mattw@codeaurora.org>
>
> It is sometimes necessary to poll a memory-mapped register until its value
> satisfies some condition. Introduce a family of convenience macros that do
> this. Tight-looping, sleeping, and timing out can all be accomplished
> using these macros.
>
...
> +#define readx_poll_timeout(op, addr, val, cond, sleep_us, timeout_us) \
> +({ \
> + ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \
> + might_sleep_if(sleep_us); \
> + for (;;) { \
> + (val) = op(addr); \
> + if (cond) \
> + break; \
> + if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) {
> \
> + (val) = op(addr); \
> + break; \
> + } \
> + if (sleep_us) \
> + usleep_range((sleep_us >> 2) + 1, sleep_us); \

The hpsa SCSI driver used to use usleep_range in a loop like
that, but we found that it caused scheduler problems during
boots because it uses TASK_UNINTERRUPTIBLE:
[ 9.260668] [sched_delayed] sched: RT throttling activated

msleep() worked much better.

---
Rob Elliott HP Server Storage





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