Commit 3beb61db authored by Geert Uytterhoeven's avatar Geert Uytterhoeven Committed by Mark Brown
Browse files

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: default avatarGeert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: default avatarMark Brown <broonie@linaro.org>
parent c9eaa447

drivers/spi/spi-rspi.c

+5 −3
Original line number Diff line number Diff line
@@ -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 */

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