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path: root/drivers/clk/rockchip/clk.c
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Diffstat (limited to 'drivers/clk/rockchip/clk.c')
-rw-r--r--drivers/clk/rockchip/clk.c36
1 files changed, 36 insertions, 0 deletions
diff --git a/drivers/clk/rockchip/clk.c b/drivers/clk/rockchip/clk.c
index fe1d393cf678..35dbd63c2f49 100644
--- a/drivers/clk/rockchip/clk.c
+++ b/drivers/clk/rockchip/clk.c
@@ -29,6 +29,7 @@
#include <linux/mfd/syscon.h>
#include <linux/regmap.h>
#include <linux/reboot.h>
+#include <linux/rational.h>
#include "clk.h"
/**
@@ -164,6 +165,40 @@ static int rockchip_clk_frac_notifier_cb(struct notifier_block *nb,
return notifier_from_errno(ret);
}
+/**
+ * fractional divider must set that denominator is 20 times larger than
+ * numerator to generate precise clock frequency.
+ */
+static void rockchip_fractional_approximation(struct clk_hw *hw,
+ unsigned long rate, unsigned long *parent_rate,
+ unsigned long *m, unsigned long *n)
+{
+ struct clk_fractional_divider *fd = to_clk_fd(hw);
+ unsigned long p_rate, p_parent_rate;
+ struct clk_hw *p_parent;
+ unsigned long scale;
+
+ p_rate = clk_hw_get_rate(clk_hw_get_parent(hw));
+ if ((rate * 20 > p_rate) && (p_rate % rate != 0)) {
+ p_parent = clk_hw_get_parent(clk_hw_get_parent(hw));
+ p_parent_rate = clk_hw_get_rate(p_parent);
+ *parent_rate = p_parent_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;
+
+ rational_best_approximation(rate, *parent_rate,
+ GENMASK(fd->mwidth - 1, 0), GENMASK(fd->nwidth - 1, 0),
+ m, n);
+}
+
static struct clk *rockchip_clk_register_frac_branch(
struct rockchip_clk_provider *ctx, const char *name,
const char *const *parent_names, u8 num_parents,
@@ -210,6 +245,7 @@ static struct clk *rockchip_clk_register_frac_branch(
div->nwidth = 16;
div->nmask = GENMASK(div->nwidth - 1, 0) << div->nshift;
div->lock = lock;
+ div->approximation = rockchip_fractional_approximation;
div_ops = &clk_fractional_divider_ops;
clk = clk_register_composite(NULL, name, parent_names, num_parents,