[PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems

Doug Anderson dianders at chromium.org
Thu May 8 17:02:02 PDT 2014


On Thu, May 8, 2014 at 1:55 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Thu, May 08, 2014 at 11:06:24AM -0700, Doug Anderson wrote:
>> I guess I would say that my patch is unhacking the this code.  The
>> code after my patch is simpler.  I would perhaps argue that (ec971ea
>> ARM: add cpufreq transiton notifier to adjust loops_per_jiffy for smp)
>> should never have landed to begin with.
> That depends on your point of view.  As I've already pointed out through
> the examples of why udelay() is inaccurate, for driver authors, they
> should assume that udelay() just gives you an "approximate" delay and
> it has no accuracy.

That disagrees with what Thomas Gleixner says at
<http://lkml.iu.edu//hypermail/linux/kernel/1203.1/01034.html>.  It
also seems like perhaps the regulator core is broken, then...  If a
udelay(30) can end up as a udelay(20) then we may return from a
regulator code 10us earlier than we should and we'll assume that a
regulator is ramped before it really is...

I'm out tomorrow but I can confirm on Monday that I was really seeing
udelay(30) be a udelay(20) without this patch.

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