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[6/8] spi: rspi: Increase bit rate range for QSPI

Message ID 20200608095940.30516-7-geert+renesas@glider.be (mailing list archive)
State Superseded
Delegated to: Geert Uytterhoeven
Headers show
Series spi: rspi: Bit rate improvements | expand

Commit Message

Geert Uytterhoeven June 8, 2020, 9:59 a.m. UTC 
Increase bit rate range for QSPI by extending the range of supported
dividers:
  1. QSPI supports a divider of 1, by setting SPBR to zero, increasing
     the upper limit from 48.75 to 97.5 MHz,
  2. Make use of the Bit Rate Frequency Division Setting field in
     Command Registers, to decrease the lower limit from 191 to 24 kbps.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
 drivers/spi/spi-rspi.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)
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Patch

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index ea3f2680d3c13e02..38c0cd7febabf114 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -334,14 +334,26 @@  static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size)
  */
 static int qspi_set_config_register(struct rspi_data *rspi, int access_size)
 {
-	int spbr;
+	unsigned long clksrc;
+	int brdv = 0, spbr;
 
 	/* Sets output mode, MOSI signal, and (optionally) loopback */
 	rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR);
 
 	/* Sets transfer bit rate */
-	spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->speed_hz);
-	rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR);
+	clksrc = clk_get_rate(rspi->clk);
+	if (rspi->speed_hz >= clksrc) {
+		spbr = 0;
+	} else {
+		spbr = DIV_ROUND_UP(clksrc, 2 * rspi->speed_hz);
+		while (spbr > 255 && brdv < 3) {
+			brdv++;
+			spbr = DIV_ROUND_UP(spbr, 2);
+		}
+		spbr = clamp(spbr, 0, 255);
+	}
+	rspi_write8(rspi, spbr, RSPI_SPBR);
+	rspi->spcmd |= SPCMD_BRDV(brdv);
 
 	/* Disable dummy transmission, set byte access */
 	rspi_write8(rspi, 0, RSPI_SPDCR);