patches.renesas/0467-spi-rspi-Round-up-division-to-avoid-slave-overclocki.patch

From a152d004374199ce599408cd03af1e9b53d3c2fa Mon Sep 17 00:00:00 2001
From: Geert Uytterhoeven <geert+renesas@glider.be>
Date: Thu, 22 May 2014 20:07:35 +0200
Subject: spi: rspi: Round up division to avoid slave overclocking

The calculation of the bit rate divider used a standard C division, which
rounds down the quotient. This may lead to a higher bitrate than requested.
Round up to avoid this.

E.g. on Koelsch, the SPI flash (configured for 30 MHz) was driven at 48.75
MHz. After this patch it's driven at a safe 24.375 MHz.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@linaro.org>
(cherry picked from commit 3beb61dbfcf188399cbc36ce1eeb8b2ba724de38)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
---
 drivers/spi/spi-rspi.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 1fb0ad213324..5639f9529e0b 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -266,7 +266,8 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size)
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
 	/* Sets transfer bit rate */
-	spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1;
+	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
+			    2 * rspi->max_speed_hz) - 1;
 	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
 
 	/* Disable dummy transmission, set 16-bit word access, 1 frame */
@@ -302,7 +303,8 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
 	/* Sets transfer bit rate */
-	spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1;
+	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk),
+			    2 * rspi->max_speed_hz) - 1;
 	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
 
 	/* Disable dummy transmission, set byte access */
@@ -335,7 +337,7 @@ static int qspi_set_config_register(struct rspi_data *rspi, int access_size)
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
 	/* Sets transfer bit rate */
-	spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz);
+	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->max_speed_hz);
 	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
 
 	/* Disable dummy transmission, set byte access */
-- 
2.1.2