[PATCH 1/5] clk: mvebu: Add core-divider clock

Hey Andrew,

On Thu, Sep 26, 2013 at 10:24:04AM +0200, Andrew Lunn wrote:

+   /*
+    * Wait for clocks to settle down, and then clear all the
+     * ratios request and the reload request.
+      */
+      udelay(1000);
+      reg &= ~(CORE_CLOCK_DIVIDER_RATIO_MASK | CORE_CLOCK_DIVIDER_RATIO_RELOAD);
+      writel(reg, corediv->reg);
+      udelay(1000);


Documentation/timers/timers-howto.txt says: 

       SLEEPING FOR ~USECS OR SMALL MSECS ( 10us - 20ms):
       		* Use usleep_range

Given the set_rate should be protected by spinlocks (as you pointed out),
I guess we can't afford using usleep_range (the context is now non-atomic).

Now, according to arch/arm/include/asm/delay.h this is the suggestion
for udelay and friends:

 * Use only for very small delays ( < 2 msec).  Should probably use a
 * lookup table, really, as the multiplications take much too long with
 * short delays.  This is a "reasonable" implementation, though (and
 * the first constant multiplications gets optimized away if the delay is
 * a constant)  

Which means we could just use udelay(1000) without much trouble.

On the other side, since we know the rate the clock is running, we could
use __delay() just as drivers/clk/sunxi/clk-factors.c is doing.
__delay() has a much simpler implementation, which feels correct in
this case of "wait until the clock settles".

Therefore, I'm currently going to try that option.
-- 
Ezequiel Garc?a, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com