From 3beb61dbfcf188399cbc36ce1eeb8b2ba724de38 Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Thu, 22 May 2014 20:07:35 +0200 Subject: [PATCH] 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 Signed-off-by: Mark Brown --- 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 1fb0ad21332..5639f9529e0 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 */ -- 2.41.0