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

[Ezequiel Garcia <ezequiel.garcia-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>]

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 García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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