* [PATCH v1 1/1] clk: fractional-divider: eliminate while-loop
@ 2015-03-19 18:54 Andy Shevchenko
2015-03-20 6:34 ` Stephen Boyd
0 siblings, 1 reply; 3+ messages in thread
From: Andy Shevchenko @ 2015-03-19 18:54 UTC (permalink / raw)
To: linux-kernel, Stephen Boyd, Heikki Krogerus; +Cc: Andy Shevchenko
We may do a calculation of the rounded rate based on (*prate / div) value in
case it is not 0. It's as much higher as power of two of nearest value to
(*prate / div / maxn). Thus, the patch replaces while-loop by direct
calculations.
While here, fix off-by-one error. maxn is the maximum value that can be hold by
a register which means all ones in it.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
drivers/clk/clk-fractional-divider.c | 13 ++++++-------
1 file changed, 6 insertions(+), 7 deletions(-)
diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index 6aa72d9..4c0541b 100644
--- a/drivers/clk/clk-fractional-divider.c
+++ b/drivers/clk/clk-fractional-divider.c
@@ -14,6 +14,7 @@
#include <linux/device.h>
#include <linux/slab.h>
#include <linux/gcd.h>
+#include <linux/log2.h>
#define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
@@ -49,18 +50,16 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
unsigned long *prate)
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
- unsigned maxn = (fd->nmask >> fd->nshift) + 1;
- unsigned div;
+ unsigned maxn = fd->nmask >> fd->nshift;
+ unsigned long div, n;
if (!rate || rate >= *prate)
return *prate;
div = gcd(*prate, rate);
-
- while ((*prate / div) > maxn) {
- div <<= 1;
- rate <<= 1;
- }
+ n = *prate / div;
+ if (n > maxn)
+ return rate * roundup_pow_of_two(n / maxn);
return rate;
}
--
2.1.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v1 1/1] clk: fractional-divider: eliminate while-loop
2015-03-19 18:54 [PATCH v1 1/1] clk: fractional-divider: eliminate while-loop Andy Shevchenko
@ 2015-03-20 6:34 ` Stephen Boyd
2015-03-20 13:03 ` Andy Shevchenko
0 siblings, 1 reply; 3+ messages in thread
From: Stephen Boyd @ 2015-03-20 6:34 UTC (permalink / raw)
To: Andy Shevchenko; +Cc: linux-kernel, Heikki Krogerus
On 03/19, Andy Shevchenko wrote:
> We may do a calculation of the rounded rate based on (*prate / div) value in
> case it is not 0. It's as much higher as power of two of nearest value to
> (*prate / div / maxn). Thus, the patch replaces while-loop by direct
> calculations.
>
> While here, fix off-by-one error. maxn is the maximum value that can be hold by
> a register which means all ones in it.
>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> ---
> drivers/clk/clk-fractional-divider.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
> index 6aa72d9..4c0541b 100644
> --- a/drivers/clk/clk-fractional-divider.c
> +++ b/drivers/clk/clk-fractional-divider.c
> @@ -14,6 +14,7 @@
> #include <linux/device.h>
> #include <linux/slab.h>
> #include <linux/gcd.h>
> +#include <linux/log2.h>
>
> #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
>
> @@ -49,18 +50,16 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
> unsigned long *prate)
> {
> struct clk_fractional_divider *fd = to_clk_fd(hw);
> - unsigned maxn = (fd->nmask >> fd->nshift) + 1;
> - unsigned div;
> + unsigned maxn = fd->nmask >> fd->nshift;
> + unsigned long div, n;
>
> if (!rate || rate >= *prate)
> return *prate;
>
> div = gcd(*prate, rate);
> -
> - while ((*prate / div) > maxn) {
> - div <<= 1;
> - rate <<= 1;
> - }
> + n = *prate / div;
> + if (n > maxn)
> + return rate * roundup_pow_of_two(n / maxn);
>
> return rate;
> }
Is there any reason why this code isn't using
rational_best_approximation() and mult_frac()?
--
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v1 1/1] clk: fractional-divider: eliminate while-loop
2015-03-20 6:34 ` Stephen Boyd
@ 2015-03-20 13:03 ` Andy Shevchenko
0 siblings, 0 replies; 3+ messages in thread
From: Andy Shevchenko @ 2015-03-20 13:03 UTC (permalink / raw)
To: Stephen Boyd; +Cc: linux-kernel, Heikki Krogerus
On Thu, 2015-03-19 at 23:34 -0700, Stephen Boyd wrote:
> On 03/19, Andy Shevchenko wrote:
> > We may do a calculation of the rounded rate based on (*prate / div) value in
> > case it is not 0. It's as much higher as power of two of nearest value to
> > (*prate / div / maxn). Thus, the patch replaces while-loop by direct
> > calculations.
> >
> > While here, fix off-by-one error. maxn is the maximum value that can be hold by
> > a register which means all ones in it.
> >
> > Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> > ---
> > drivers/clk/clk-fractional-divider.c | 13 ++++++-------
> > 1 file changed, 6 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
> > index 6aa72d9..4c0541b 100644
> > --- a/drivers/clk/clk-fractional-divider.c
> > +++ b/drivers/clk/clk-fractional-divider.c
> > @@ -14,6 +14,7 @@
> > #include <linux/device.h>
> > #include <linux/slab.h>
> > #include <linux/gcd.h>
> > +#include <linux/log2.h>
> >
> > #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
> >
> > @@ -49,18 +50,16 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
> > unsigned long *prate)
> > {
> > struct clk_fractional_divider *fd = to_clk_fd(hw);
> > - unsigned maxn = (fd->nmask >> fd->nshift) + 1;
> > - unsigned div;
> > + unsigned maxn = fd->nmask >> fd->nshift;
> > + unsigned long div, n;
> >
> > if (!rate || rate >= *prate)
> > return *prate;
> >
> > div = gcd(*prate, rate);
> > -
> > - while ((*prate / div) > maxn) {
> > - div <<= 1;
> > - rate <<= 1;
> > - }
> > + n = *prate / div;
> > + if (n > maxn)
> > + return rate * roundup_pow_of_two(n / maxn);
> >
> > return rate;
> > }
>
> Is there any reason why this code isn't using
> rational_best_approximation() and mult_frac()?
For fist glance it should be faster that rational_best_approximation(),
though less precise.
I could switch to them.
--
Andy Shevchenko <andriy.shevchenko@intel.com>
Intel Finland Oy
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