[RFC PATCH 2/5] clk: Introduce 'clk_round_rate_nearest()'

[Sören Brinkmann]

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.brinkmann at 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-koenig at pengutronix.de>
Signed-off-by: Soren Brinkmann <soren.brinkmann at 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