Re: [PATCH] brcmfmac: cfg80211: use msecs_to_jiffies for time conversion

From: Joe Perches
Date: Wed Mar 18 2015 - 03:31:13 EST

On Wed, 2015-03-18 at 07:44 +0100, Nicholas Mc Guire wrote:
> On Tue, 17 Mar 2015, Joe Perches wrote:
> > On Tue, 2015-03-17 at 08:06 -0400, Nicholas Mc Guire wrote:
> > > Converting milliseconds to jiffies by "val * HZ / 1000" is technically
> > > OK but msecs_to_jiffies(val) is the cleaner solution and handles all
> > > corner cases correctly. This is a minor API consolidation only and
> > > should make things more readable.

> > These API consolidation changes now always have a function
> > call when the compiler may have previously been able to
> > optimize out the "constant * HZ / 1000" calculation.
> >
> > Perhaps the [um]secs_to_jiffies calls should be indirected
> > with yet another static inline with a __builtin_constant_p()
> > test so that the function calls can again be avoided when
> > possible.
> will give it a try

OK, thanks.

The tricky bit seems to be the movement of
the Makefile for kernel/time/timeconst.h.

BC kernel/time/timeconst.h

as include/linux/time.h would need these
calculated #defines

#define MSEC_TO_HZ_MUL32 U64_C(0x80000000)
#define MSEC_TO_HZ_ADJ32 U64_C(0x0)
#define MSEC_TO_HZ_SHR32 31

and the usec ones too.

That created file would have to be moved from
kernel/time/Makefile to some other location
that could be in the normal include path like
include/linux/timeconst.h so that it can be
used by include/linux/time.h

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