From feace90233a8cd44a18902216657279c3932d471 Mon Sep 17 00:00:00 2001 From: Geert Uytterhoeven Date: Wed, 19 Aug 2020 14:59:00 +0200 Subject: [PATCH] spi: rspi: Increase bit rate accuracy on RZ/A rspi_rz_set_config_register() favors high values of "brdv" over high values of "spbr". As "brdv" is not a plain divider, but controls a power-of-two divider, this may cause the selection of non-optimal divider values. E.g. on RSK+RZA1, when 3.8 MHz is requested, the actual configured bit rate is 2.08 MHz (spbr = 1, brdv = 3), while 3.7 MHz would be possible (spbr = 8, brdv = 0). Fix this by only resorting to higher "brdv" values when really needed. This makes the driver always pick optimal divider values on RZ/A. Signed-off-by: Geert Uytterhoeven Link: https://lore.kernel.org/r/20200819125904.20938-4-geert+renesas@glider.be Signed-off-by: Mark Brown --- drivers/spi/spi-rspi.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 450a42e..ad4ac86 100644 --- a/drivers/spi/spi-rspi.c +++ b/drivers/spi/spi-rspi.c @@ -298,15 +298,13 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); clksrc = clk_get_rate(rspi->clk); - while (brdv < 3) { - if (rspi->speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */ - break; + spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; + while (spbr > 255 && brdv < 3) { brdv++; - clksrc /= 2; + spbr = DIV_ROUND_UP(spbr + 1, 2) - 1; } /* Sets transfer bit rate */ - spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); rspi->spcmd |= SPCMD_BRDV(brdv); -- 2.7.4