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path: root/drivers/clk/clk-fractional-divider.c
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Diffstat (limited to 'drivers/clk/clk-fractional-divider.c')
-rw-r--r--drivers/clk/clk-fractional-divider.c53
1 files changed, 33 insertions, 20 deletions
diff --git a/drivers/clk/clk-fractional-divider.c b/drivers/clk/clk-fractional-divider.c
index e85f856b8..5c4955e33 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)
@@ -22,7 +23,8 @@ static unsigned long clk_fd_recalc_rate(struct clk_hw *hw,
{
struct clk_fractional_divider *fd = to_clk_fd(hw);
unsigned long flags = 0;
- u32 val, m, n;
+ unsigned long m, n;
+ u32 val;
u64 ret;
if (fd->lock)
@@ -50,23 +52,33 @@ 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 = (fd->nmask >> fd->nshift) + 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 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 ((*prate / div) > maxn) {
- div <<= 1;
- rate <<= 1;
- }
+ rational_best_approximation(rate, *parent_rate,
+ GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
+ &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,
@@ -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);
unsigned long flags = 0;
- unsigned long div;
- unsigned n, m;
+ unsigned long m, n;
u32 val;
- div = gcd(parent_rate, rate);
- m = rate / div;
- n = parent_rate / div;
+ rational_best_approximation(rate, parent_rate,
+ GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
+ &m, &n);
if (fd->lock)
spin_lock_irqsave(fd->lock, flags);
@@ -128,9 +139,11 @@ 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;
fd->flags = clk_divider_flags;
fd->lock = lock;
fd->hw.init = &init;