From: Geert Uytterhoeven <geert+renesas@glider.be>
To: Mark Brown <broonie@kernel.org>
Cc: Chris Brandt <chris.brandt@renesas.com>,
linux-spi@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
linux-sh@vger.kernel.org,
Geert Uytterhoeven <geert+renesas@glider.be>
Subject: [PATCH v2 3/7] spi: rspi: Increase bit rate accuracy on RZ/A
Date: Wed, 19 Aug 2020 12:59:00 +0000 [thread overview]
Message-ID: <20200819125904.20938-4-geert+renesas@glider.be> (raw)
In-Reply-To: <20200819125904.20938-1-geert+renesas@glider.be>
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>
---
v2:
- No changes.
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
next prev parent reply other threads:[~2020-08-19 12:59 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-19 12:58 [PATCH v2 0/7] spi: rspi: Bit rate improvements Geert Uytterhoeven
2020-08-19 12:58 ` [PATCH v2 1/7] spi: rspi: Remove useless .set_config_register() check Geert Uytterhoeven
2020-08-19 12:58 ` [PATCH v2 2/7] spi: rspi: Clean up Bit Rate Division Setting handling Geert Uytterhoeven
2020-08-19 12:59 ` Geert Uytterhoeven [this message]
2020-08-19 12:59 ` [PATCH v2 4/7] spi: rspi: Increase bit rate range for RSPI on SH Geert Uytterhoeven
2020-08-19 12:59 ` [PATCH v2 5/7] spi: rspi: Increase bit rate range for QSPI Geert Uytterhoeven
2020-08-19 12:59 ` [PATCH v2 6/7] spi: rspi: Fill in spi_transfer.effective_speed_hz Geert Uytterhoeven
2020-08-19 12:59 ` [PATCH v2 7/7] spi: rspi: Fill in controller speed limits Geert Uytterhoeven
2020-08-20 21:48 ` [PATCH v2 0/7] spi: rspi: Bit rate improvements Mark Brown
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