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Subject[PATCH 1/4] clk: Introduce 'clk_find_nearest_rate()'
Date
Introduce a new API function to find the rate a clock can provide which
is closest to a given rate.

clk_round_rate() leaves it to the clock driver how rounding is done.
Commonly implementations round down due to use-cases that have a certain
frequency maximum that must not be exceeded.

The new API call enables use-cases where accuracy is preferred. E.g.
Ethernet clocks.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
---

drivers/clk/clk.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/clk.h | 9 +++++++++
2 files changed, 66 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 8b73edef151d..fce1165cd879 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1030,6 +1030,63 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
EXPORT_SYMBOL_GPL(clk_round_rate);

/**
+ * clk_find_nearest_rate - round the given rate for a clk
+ * @clk: the clk for which we are rounding a rate
+ * @rate: the rate which is to be rounded
+ *
+ * Takes in a rate as input and finds the closest rate that the clk
+ * can actually use which is then returned.
+ * Note: This function relies on the clock's clk_round_rate() implementation.
+ * For cases clk_round_rate() rounds up, not the closest but the rounded up
+ * rate is found.
+ */
+long clk_find_nearest_rate(struct clk *clk, unsigned long rate)
+{
+ long ret, lower, upper;
+ unsigned long tmp;
+
+ clk_prepare_lock();
+
+ lower = __clk_round_rate(clk, rate);
+ if (lower >= rate || lower < 0) {
+ ret = lower;
+ goto unlock;
+ }
+
+ tmp = rate + (rate - lower) - 1;
+ if (tmp > LONG_MAX)
+ upper = LONG_MAX;
+ else
+ upper = tmp;
+
+ upper = __clk_round_rate(clk, upper);
+ if (upper <= lower || upper < 0) {
+ ret = lower;
+ goto unlock;
+ }
+
+ lower = rate + 1;
+ while (lower < upper) {
+ long rounded, mid;
+
+ mid = lower + ((upper - lower) >> 1);
+ rounded = __clk_round_rate(clk, mid);
+ if (rounded < lower)
+ lower = mid + 1;
+ else
+ upper = rounded;
+ }
+
+ ret = upper;
+
+unlock:
+ clk_prepare_unlock();
+
+ return ret;
+}
+EXPORT_SYMBOL_GPL(clk_find_nearest_rate);
+
+/**
* __clk_notify - call clk notifier chain
* @clk: struct clk * that is changing rate
* @msg: clk notifier type (see include/linux/clk.h)
diff --git a/include/linux/clk.h b/include/linux/clk.h
index fb5e097d8f72..f8b53c515483 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -264,6 +264,15 @@ void devm_clk_put(struct device *dev, struct clk *clk);
long clk_round_rate(struct clk *clk, unsigned long rate);

/**
+ * clk_find_nearest_rate - Find nearest rate to the exact rate a clock can provide
+ * @clk: the clk for which we are rounding a rate
+ * @rate: the rate which is to be rounded
+ *
+ * Returns the rate closest to @rate the clock can provide.
+ */
+long clk_find_nearest_rate(struct clk *clk, unsigned long rate);
+
+/**
* clk_set_rate - set the clock rate for a clock source
* @clk: clock source
* @rate: desired clock rate in Hz
--
2.0.1.1.gfbfc394


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