[ath9k-devel] [PATCH 1/3] ath9k: Fix build error on ARM

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Wed, Feb 05, 2014 at 06:03:13AM -0800, Joe Perches wrote:
> On Wed, 2014-02-05 at 13:39 +0000, Russell King - ARM Linux wrote:
> > On Wed, Feb 05, 2014 at 05:04:54AM -0800, Joe Perches wrote:
> > > On Wed, 2014-02-05 at 12:41 +0000, Russell King - ARM Linux wrote:
> > > > On Wed, Feb 05, 2014 at 04:32:46AM -0800, Joe Perches wrote:
> > > > > Apparently, people just convert stupidly large udelay()s
> > > > > to mdelay and not be bothered.
> > > > 
> > > > And that's the correct answer.  Having udelay(10000) rather than mdelay(10)
> > > > is a sign that they weren't paying that much attention when writing the
> > > > code.
> > > 
> > > Not really.
> []
> > > It's not so much not paying attention as not
> > > knowing ARM is broken for large udelay().
> > 
> > And now read my suggestion about how to avoid the "not knowing" problem. :)
> 
> I'd read it already.  I didn't and don't disagree.

Please explain /why/ you don't agree.

> I still think adding a #warning on large static udelay()s
> would be sensible.  Maybe adding another option like
> #define UDELAY_TOO_BIG_I_KNOW_ALREADY_DONT_BOTHER_ME
> guard to avoid seeing the #warning when there's no other
> option.

How does that help?  It's /not/ a warning situation - if you ask for
udelay(10000) on ARM, you will /not/ get a 10ms delay.  You'll instead
get something much shorter because the arithmetic will overflow.

Now, you could argue that maybe ARM's udelay() implementation should
know about this and implement a loop around the underlying udelay()
implementation to achieve it, and I might agree with you - but I
don't for one very simple reason: we /already/ have such an
implementation.  It's called mdelay():

#ifndef mdelay
#define mdelay(n) (\
        (__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
        ({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
#endif

So, the right answer is /not/ do duplicate this, but to /use/ the
appropriate facilities provided by the kernel.

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