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 <geert+renesas@xxxxxxxxx>
---
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 450a42ec2141a895..ad4ac867170b101a 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);
--
2.17.1
