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spi: rspi: Round up division to avoid slave overclocking

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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>
Signed-off-by: Mark Brown <broonie@linaro.org>
This commit is contained in:
Geert Uytterhoeven 2014-05-22 20:07:35 +02:00 committed by Mark Brown
parent c9eaa447e7
commit 3beb61dbfc
1 changed files with 5 additions and 3 deletions
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8
drivers/spi/spi-rspi.c
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@ -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 */