timer: add fsleep for flexible sleeping

Sleeping for a certain amount of time requires use of different
functions, depending on the time period.
Documentation/timers/timers-howto.rst explains when to use which
function, and also checkpatch checks for some potentially
problematic cases.

So let's create a helper that automatically chooses the appropriate
sleep function -> fsleep(), for flexible sleeping

If the delay is a constant, then the compiler should be able to ensure
that the new helper doesn't create overhead. If the delay is not
constant, then the new helper can save some code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/timers/timers-howto.rst b/Documentation/timers/timers-howto.rst
index 7e3167bec2b1ff96c961609cd75a098665497375..afb0a43b8cdfb69853664bd5544860265ddfeb0c 100644 (file)
--- a/Documentation/timers/timers-howto.rst
+++ b/Documentation/timers/timers-howto.rst
@@ -110,3 +110,6 @@ NON-ATOMIC CONTEXT:
                        short, the difference is whether the sleep can be ended
                        early by a signal. In general, just use msleep unless
                        you know you have a need for the interruptible variant.
+
+       FLEXIBLE SLEEPING (any delay, uninterruptible)
+               * Use fsleep

diff --git a/include/linux/delay.h b/include/linux/delay.h
index 8e6828094c1ee1bc6aebfc1d1a55ccaecf29a5c6..5e016a4029d9cb7325ddcbd4a66a87d13b818591 100644 (file)
--- a/include/linux/delay.h
+++ b/include/linux/delay.h
@@ -65,4 +65,15 @@ static inline void ssleep(unsigned int seconds)
        msleep(seconds * 1000);
 }
 
+/* see Documentation/timers/timers-howto.rst for the thresholds */
+static inline void fsleep(unsigned long usecs)
+{
+       if (usecs <= 10)
+               udelay(usecs);
+       else if (usecs <= 20000)
+               usleep_range(usecs, 2 * usecs);
+       else
+               msleep(DIV_ROUND_UP(usecs, 1000));
+}
+
 #endif /* defined(_LINUX_DELAY_H) */