This patch converts the code to use rational best approximation algorithm which is more precise.
Suggested-by: Stephen Boyd <[email protected]> Signed-off-by: Andy Shevchenko <[email protected]> --- drivers/clk/Kconfig | 1 + drivers/clk/clk-fractional-divider.c | 38 +++++++++++++++++++++--------------- 2 files changed, 23 insertions(+), 16 deletions(-) diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig index 0b474a0..3a1b1dc 100644 --- a/drivers/clk/Kconfig +++ b/drivers/clk/Kconfig @@ -14,6 +14,7 @@ config COMMON_CLK select HAVE_CLK_PREPARE select CLKDEV_LOOKUP select SRCU + select RATIONAL ---help--- The common clock framework is a single definition of struct clk, useful across many platforms, as well as an diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c index 23a56a0..f060be8 100644 --- a/drivers/clk/clk-fractional-divider.c +++ b/drivers/clk/clk-fractional-divider.c @@ -7,13 +7,14 @@ * * Adjustable fractional divider clock implementation. * Output rate = (m / n) * parent_rate. + * Uses rational best approximation algorithm. */ #include <linux/clk-provider.h> #include <linux/module.h> #include <linux/device.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) @@ -47,23 +48,29 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw, } static long clk_fd_round_rate(struct clk_hw *hw, unsigned long rate, - unsigned long *prate) + unsigned long *parent_rate) { struct clk_fractional_divider *fd = to_clk_fd(hw); - unsigned maxn = clk_div_mask(fd->nwidth) + 1; - unsigned div; + unsigned long scale; + unsigned long m, n; + u64 ret; - if (!rate || rate >= *prate) - return *prate; + if (!rate || rate >= *parent_rate) + return *parent_rate; - div = gcd(*prate, rate); + /* Get rate closer to *parent_rate */ + scale = fls_long(*parent_rate / rate - 1); + if (scale > fd->nwidth) + rate <<= scale - fd->nwidth; - while ((*prate / div) > maxn) { - div <<= 1; - rate <<= 1; - } + rational_best_approximation(rate, *parent_rate, + clk_div_mask(fd->mwidth), clk_div_mask(fd->nwidth), + &m, &n); - return rate; + ret = (u64)*parent_rate * m; + do_div(ret, n); + + return ret; } static void clk_fd_update(struct clk_fractional_divider *fd, @@ -82,12 +89,11 @@ static int clk_fd_set_rate(struct clk_hw *hw, unsigned long rate, { struct clk_fractional_divider *fd = to_clk_fd(hw); unsigned long flags; - unsigned long div; unsigned long m, n; - div = gcd(parent_rate, rate); - m = rate / div; - n = parent_rate / div; + rational_best_approximation(rate, parent_rate, + clk_div_mask(fd->mwidth), clk_div_mask(fd->nwidth), + &m, &n); if (fd->lock) { spin_lock_irqsave(fd->lock, flags); -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
