On 19/02/18 11:32, Arnd Bergmann wrote: > On Tue, Jan 2, 2018 at 3:42 PM, Sudeep Holla <[email protected]> wrote: > >> +#define SCMI_MAX_POLLING_TIMEOUT_NS (100 * NSEC_PER_USEC) >> /** >> * scmi_do_xfer() - Do one transfer >> * >> @@ -389,14 +406,30 @@ int scmi_do_xfer(const struct scmi_handle *handle, >> struct scmi_xfer *xfer) > >> + if (xfer->hdr.poll_completion) { >> + ktime_t stop, cur; >> + >> + stop = ktime_add_ns(ktime_get(), >> SCMI_MAX_POLLING_TIMEOUT_NS); >> + do { >> + udelay(5); >> + cur = ktime_get(); >> + } while (!scmi_xfer_poll_done(info, xfer) && >> + ktime_before(cur, stop)); > > The 5 microsecond back-off isn't that much smaller than the 100 microsecond > timeout, given that udelay() often waits much longer than the specified time. > > How did you come up with those two numbers? Are you sure this is better > than just using a cpu_relax() instead of the udelay()? >
Somehow I assumed that cpu_relax will schedule out and since this is called in the fast switching path, I can't do that. But now I see that it's just an hint and so I can use it. Sorry for missing it earlier, you did point this out in previous version and I retained it based on my wrong assumption. Thanks. -- Regards, Sudeep
