On Tue, 2015-07-21 at 17:41 -0700, Stephen Boyd wrote:
> On 07/14, Andy Shevchenko wrote:
> > diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk
> > -fractional-divider.c
> > index 7cfcc56..16f42ae 100644
> > --- a/drivers/clk/clk-fractional-divider.c
> > +++ b/drivers/clk/clk-fractional-divider.c
> > @@ -128,9 +128,11 @@ struct clk
> > *clk_register_fractional_divider(struct device *dev,
> >
> > fd->reg = reg;
> > fd->mshift = mshift;
> > - fd->mmask = (BIT(mwidth) - 1) << mshift;
> > + fd->mwidth = mwidth;
> > + fd->mmask = GENMASK(mwidth - 1, 0) << mshift;
> > fd->nshift = nshift;
> > - fd->nmask = (BIT(nwidth) - 1) << nshift;
> > + fd->nwidth = nwidth;
> > + fd->nmask = GENMASK(nwidth - 1, 0) << nshift;
>
> Please do the shifts in the GENMASK.
It's not optimal. Waste of performance.
32-bit case on 32-bit machine (similar to other cases on x86).
a) GENMASK(x - 1, 0) << y
movl $32, %ecx
subb 4(%esp), %cl
movl $-1, %eax
shrl %cl, %eax
movzbl 8(%esp), %ecx
sall %cl, %eax
ret
b) GENMASK(x + y - 1, y)
pushl %esi
pushl %ebx
movl $1, %edx
movzbl 12(%esp), %eax
movzbl 16(%esp), %esi
movl $-1, %ebx
subl %eax, %edx
movl %ebx, %eax
subl %esi, %edx
leal 31(%edx), %ecx
shrl %cl, %eax
movl %esi, %ecx
sall %cl, %ebx
andl %ebx, %eax
popl %ebx
popl %esi
ret
--
Andy Shevchenko <andriy.shevche...@linux.intel.com>
Intel Finland Oy
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