From mboxrd@z Thu Jan 1 00:00:00 1970 From: Chris Brandt Subject: [PATCH] spi: rspi: Increase accuracy of bit rate for RZ Date: Fri, 5 Aug 2016 09:36:03 -0400 Message-ID: <1470404163-27427-1-git-send-email-chris.brandt@renesas.com> Cc: Chris Brandt , linux-spi@vger.kernel.org, linux-renesas-soc@vger.kernel.org, Geert Uytterhoeven , Daniel Palmer To: broonie@kernel.org Return-path: Sender: linux-renesas-soc-owner@vger.kernel.org List-Id: linux-spi.vger.kernel.org When you leave the clock divider at 0, 130kHz is the lowest you can go. Also, by adjusting the clock divider you can get more accurate resolutions for clock speeds lower than 16MHz. This patch uses the clock divider as part of the bit rate setup. Signed-off-by: Chris Brandt --- drivers/spi/spi-rspi.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 8188433..a816f07 100644 --- a/drivers/spi/spi-rspi.c +++ b/drivers/spi/spi-rspi.c @@ -295,14 +295,24 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size) static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) { int spbr; + int div = 0; + unsigned long clksrc; /* Sets output mode, MOSI signal, and (optionally) loopback */ rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); + clksrc = clk_get_rate(rspi->clk); + while (div < 3) { + if (rspi->max_speed_hz >= clksrc/4) /* 4=(CLK/2)/2 */ + break; + div++; + clksrc /= 2; + } + /* Sets transfer bit rate */ - spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), - 2 * rspi->max_speed_hz) - 1; + spbr = DIV_ROUND_UP(clksrc, 2 * rspi->max_speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); + rspi->spcmd |= div << 2; /* Disable dummy transmission, set byte access */ rspi_write8(rspi, SPDCR_SPLBYTE, RSPI_SPDCR); -- 1.9.1