Merge branch 'timer-add-fsleep-for-flexible-sleeping'

Heiner Kallweit says:

====================
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
Not sure why such a helper doesn't exist yet, or where the pitfall is,
because it's a quite obvious idea.

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.

First user is the r8169 network driver. If nothing speaks against it,
then this series could go through the netdev tree.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

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

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) */