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| author | Geert Uytterhoeven <geert+renesas@glider.be> | 2020-08-19 14:59:00 +0200 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2020-08-20 22:38:13 +0100 |
| commit | feace90233a8cd44a18902216657279c3932d471 (patch) | |
| tree | dd76fa433e164725fc2f940b1fa265b9f76e768e /drivers/spi/spi-rspi.c | |
| parent | 8dd71698607f822c3675c366a8a79bc82f7621f8 (diff) | |
| download | lwn-feace90233a8cd44a18902216657279c3932d471.tar.gz lwn-feace90233a8cd44a18902216657279c3932d471.zip | |
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 <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200819125904.20938-4-geert+renesas@glider.be
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi/spi-rspi.c')
| -rw-r--r-- | drivers/spi/spi-rspi.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 450a42ec2141..ad4ac867170b 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); |