Messages in this thread | | | Date | Tue, 7 Jul 2015 16:26:18 -0700 | From | Stephen Boyd <> | Subject | Re: [PATCH v3 1/7] clk: introduce clk_div_mask() helper |
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On 07/07, Andy Shevchenko wrote: > On Thu, 2015-06-18 at 12:48 -0700, Stephen Boyd wrote: > > On 03/31, Andy Shevchenko wrote: > > > diff --git a/include/linux/clk-provider.h b/include/linux/clk > > > -provider.h > > > index 5591ea7..20b0b67 100644 > > > --- a/include/linux/clk-provider.h > > > +++ b/include/linux/clk-provider.h > > > @@ -353,6 +353,11 @@ struct clk_divider { > > > spinlock_t *lock; > > > }; > > > > > > +static inline unsigned long clk_div_mask(u8 width) > > > +{ > > > + return (1 << width) - 1; > > > +} > > > + > > > > Why not just change drivers to use GENMASK? It's a proven and > > tested way to generate a bitmask. > > Too many unneeded calculations I suppose.
That's what compiler optimizations are for.
> > Compare: > mask = clk_div_mask(mm) << ms; > which is simple ((1 << mm) - 1) << ms > and > mask = GENMASK(mm + ms - 1, ms); > which is (~0 << ms) & (~0 >> (BITS_PER_LONG - 1 - (mm + ms - > 1)))
And if mm is 32 then we hit undefined behavior.
> > > > > So I'd rather see drivers converted to use that macro directly > > especially because the mask may need to start at some bit that > > isn't 0. > > If you think the above is not a burden, I can do the conversion to > GENMASK. > > Though it might make sense when ms = 0 explicitly. >
Yes let's use GENMASK. I imagine the extra few instructions are negligible.
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