patches.renesas/0067-i2c-rcar-get-clock-rate-only-once-and-simplify-calcu.patch

From b90b58f17c718c41bba0d00349e05b03c6bbddb9 Mon Sep 17 00:00:00 2001
From: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Date: Thu, 12 Sep 2013 14:36:45 +0200
Subject: i2c: rcar: get clock rate only once and simplify calculation

There is no need to repeatedly query clock frequency, where it is not
expected to change. The complete loop can also trivially be replaced with
a simple division. A further loop below the one, being simplified, could
also be replaced, but that would get more complicated.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski+renesas@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
(cherry picked from commit 8d0494037bb2af32a22563d40703c1263fca318d)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
---
 drivers/i2c/busses/i2c-rcar.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/drivers/i2c/busses/i2c-rcar.c b/drivers/i2c/busses/i2c-rcar.c
index e295f6044dbb..39e9739f58b2 100644
--- a/drivers/i2c/busses/i2c-rcar.c
+++ b/drivers/i2c/busses/i2c-rcar.c
@@ -231,6 +231,7 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv,
 	u32 round, ick;
 	u32 scl;
 	u32 cdf_width;
+	unsigned long rate;
 
 	if (!clkp) {
 		dev_err(dev, "there is no peripheral_clk\n");
@@ -264,15 +265,14 @@ static int rcar_i2c_clock_calculate(struct rcar_i2c_priv *priv,
 	 * clkp : peripheral_clk
 	 * F[]  : integer up-valuation
 	 */
-	for (cdf = 0; cdf < (1 << cdf_width); cdf++) {
-		ick = clk_get_rate(clkp) / (1 + cdf);
-		if (ick < 20000000)
-			goto ick_find;
+	rate = clk_get_rate(clkp);
+	cdf = rate / 20000000;
+	if (cdf >= 1 << cdf_width) {
+		dev_err(dev, "Input clock %lu too high\n", rate);
+		return -EIO;
 	}
-	dev_err(dev, "there is no best CDF\n");
-	return -EIO;
+	ick = rate / (cdf + 1);
 
-ick_find:
 	/*
 	 * it is impossible to calculate large scale
 	 * number on u32. separate it
@@ -290,6 +290,12 @@ ick_find:
 	 *
 	 * Calculation result (= SCL) should be less than
 	 * bus_speed for hardware safety
+	 *
+	 * We could use something along the lines of
+	 *	div = ick / (bus_speed + 1) + 1;
+	 *	scgd = (div - 20 - round + 7) / 8;
+	 *	scl = ick / (20 + (scgd * 8) + round);
+	 * (not fully verified) but that would get pretty involved
 	 */
 	for (scgd = 0; scgd < 0x40; scgd++) {
 		scl = ick / (20 + (scgd * 8) + round);
-- 
1.8.5.rc3