Messages in this thread Patch in this message | | | From | Geert Uytterhoeven <> | Subject | [PATCH] spi: rspi: Round up division to avoid slave overclocking | Date | Thu, 22 May 2014 20:07:35 +0200 |
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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> --- Simon: I think you want this in renesas-backports.
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 */ -- 1.9.1
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