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clk: fractional-divider: switch to rational best approximation

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This patch converts the code to use rational best approximation algorithm which
is much more precise.

Suggested-by: Stephen Boyd <sboyd@codeaurora.org>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
This commit is contained in:
Andy Shevchenko 2015-09-22 18:54:11 +03:00 • committed by Stephen Boyd
parent 5d49a6e103
commit 0777591e71
2 changed files with 27 additions and 15 deletions
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1
drivers/clk/Kconfig
View file

@ -14,6 +14,7 @@ config COMMON_CLK
select HAVE_CLK_PREPARE select HAVE_CLK_PREPARE
select CLKDEV_LOOKUP select CLKDEV_LOOKUP
select SRCU select SRCU
select RATIONAL
---help--- ---help---
The common clock framework is a single definition of struct The common clock framework is a single definition of struct
clk, useful across many platforms, as well as an clk, useful across many platforms, as well as an

41
drivers/clk/clk-fractional-divider.c
View file

@ -7,13 +7,14 @@
* *
* Adjustable fractional divider clock implementation. * Adjustable fractional divider clock implementation.
* Output rate = (m / n) * parent_rate. * Output rate = (m / n) * parent_rate.
* Uses rational best approximation algorithm.
*/ */
#include <linux/clk-provider.h> #include <linux/clk-provider.h>
#include <linux/module.h> #include <linux/module.h>
#include <linux/device.h> #include <linux/device.h>
#include <linux/slab.h> #include <linux/slab.h>
#include <linux/gcd.h> #include <linux/rational.h>
#define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw) #define to_clk_fd(_hw) container_of(_hw, struct clk_fractional_divider, hw)
@ -22,7 +23,8 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
{ {
struct clk_fractional_divider *fd = to_clk_fd(hw); struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long flags = 0; unsigned long flags = 0;
u32 val, m, n; unsigned long m, n;
u32 val;
u64 ret; u64 ret;
if (fd->lock) if (fd->lock)
@ -53,20 +55,30 @@ static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate,
unsigned long *parent_rate) unsigned long *parent_rate)
{ {
struct clk_fractional_divider *fd = to_clk_fd(hw); struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned maxn = (fd->nmask >> fd->nshift) + 1; unsigned long scale;
unsigned div; unsigned long m, n;
u64 ret;
if (!rate || rate >= *parent_rate) if (!rate || rate >= *parent_rate)
return *parent_rate; return *parent_rate;
div = gcd(*parent_rate, rate); /*
* Get rate closer to *parent_rate to guarantee there is no overflow
* for m and n. In the result it will be the nearest rate left shifted
* by (scale - fd->nwidth) bits.
*/
scale = fls_long(*parent_rate / rate - 1);
if (scale > fd->nwidth)
rate <<= scale - fd->nwidth;
while ((*parent_rate / div) > maxn) { rational_best_approximation(rate, *parent_rate,
div <<= 1; GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
rate <<= 1; &m, &n);
}
return rate; ret = (u64)*parent_rate * m;
do_div(ret, n);
return ret;
} }
static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate, static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
@ -74,13 +86,12 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate,
{ {
struct clk_fractional_divider *fd = to_clk_fd(hw); struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long flags = 0; unsigned long flags = 0;
unsigned long div; unsigned long m, n;
unsigned n, m;
u32 val; u32 val;
div = gcd(parent_rate, rate); rational_best_approximation(rate, parent_rate,
m = rate / div; GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
n = parent_rate / div; &m, &n);
if (fd->lock) if (fd->lock)
spin_lock_irqsave(fd->lock, flags); spin_lock_irqsave(fd->lock, flags);