Hi,
I spent some time finding an alternative implementation for
clk_round_rate_nearest, the result can be found below.
I hope this is closer to a working implementation.
Thanks,
Sören
------------------8<-----------------8<---------------------8<-------------8<---
From: Soren Brinkmann <soren.brinkm...@xilinx.com>
Date: Tue, 2 Apr 2013 10:08:13 -0700
Subject: [PATCH] clk: Introduce 'clk_round_rate_nearest()'
Introduce a new API function to round a rate to the closest possible
rate the HW clock can generate.
In contrast to 'clk_round_rate()' which works similar, but always returns
a frequency <= its input rate.
Cc: Uwe Kleine-König <u.kleine-koe...@pengutronix.de>
Signed-off-by: Soren Brinkmann <soren.brinkm...@xilinx.com>
---
drivers/clk/clk.c | 43 +++++++++++++++++++++++++++++++++++++++++--
include/linux/clk.h | 14 ++++++++++++--
2 files changed, 53 insertions(+), 4 deletions(-)
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index dff0373f53c1..faf24d0569df 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1011,8 +1011,9 @@ unsigned long __clk_round_rate(struct clk *clk, unsigned
long rate)
* @rate: the rate which is to be rounded
*
* Takes in a rate as input and rounds it to a rate that the clk can actually
- * use which is then returned. If clk doesn't support round_rate operation
- * then the parent rate is returned.
+ * use and does not exceed the requested frequency, which is then returned.
+ * If clk doesn't support round_rate operation then the parent rate
+ * is returned.
*/
long clk_round_rate(struct clk *clk, unsigned long rate)
{
@@ -1027,6 +1028,44 @@ long clk_round_rate(struct clk *clk, unsigned long rate)
EXPORT_SYMBOL_GPL(clk_round_rate);
/**
+ * clk_round_rate_nearest - 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 rounds it to the closest rate that the clk
+ * can actually use which is then returned. If clk doesn't support
+ * round_rate operation then the parent rate is returned.
+ */
+long clk_round_rate_nearest(struct clk *clk, unsigned long rate)
+{
+ unsigned long lower, upper, cur, lower_last, upper_last;
+
+ lower = clk_round_rate(clk, rate);
+ if (lower >= rate)
+ return lower;
+
+ upper = clk_round_rate(clk, rate + rate - lower);
+ if (upper == lower)
+ return upper;
+
+ lower = rate + 1;
+ do {
+ upper_last = upper;
+ lower_last = lower;
+
+ cur = clk_round_rate(clk, lower + ((upper - lower) >> 1));
+ if (cur < lower)
+ lower += (upper - lower) >> 1;
+ else
+ upper = cur;
+
+ } while (lower_last != lower && upper_last != upper);
+
+ return upper;
+}
+EXPORT_SYMBOL_GPL(clk_round_rate_nearest);
+
+/**
* __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..2f83bf030ac6 100644
--- a/include/linux/clk.h
+++ b/include/linux/clk.h
@@ -255,15 +255,25 @@ void devm_clk_put(struct device *dev, struct clk *clk);
/**
- * clk_round_rate - adjust a rate to the exact rate a clock can provide
+ * clk_round_rate - round a rate to the exact rate a clock can provide not
+ * exceeding @rate
* @clk: clock source
* @rate: desired clock rate in Hz
*
- * Returns rounded clock rate in Hz, or negative errno.
+ * Returns rounded clock rate in Hz, or parent rate
*/
long clk_round_rate(struct clk *clk, unsigned long rate);
/**
+ * clk_round_rate_nearest - round a 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 rounded clock rate in Hz, or parent rate
+ */
+long clk_round_rate_nearest(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
--
1.9.3.1.ga73a6ad
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