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spi: rspi: Increase bit rate range for QSPI

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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 on R-Car Gen2,
  2. Make use of the Bit Rate Frequency Division Setting field in
     Command Registers, to decrease the lower limit from 191 to 24 kbps
     on R-Car Gen2.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200819125904.20938-6-geert+renesas@glider.be
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Geert Uytterhoeven 2020-08-19 14:59:02 +02:00 committed by Mark Brown
parent 4e71d926ab
commit 6a195f24f3
No known key found for this signature in database
GPG key ID: 24D68B725D5487D0
1 changed files with 15 additions and 3 deletions
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18
drivers/spi/spi-rspi.c
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@ -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);