| Message ID | 1400782055-19609-1-git-send-email-geert+renesas@glider.be (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 3beb61dbfcf188399cbc36ce1eeb8b2ba724de38 |
| Headers | show |
On Thu, May 22, 2014 at 08:07:35PM +0200, Geert Uytterhoeven wrote: > The calculation of the bit rate divider used a standard C division, which > rounds down the quotient. This may lead to a higher bitrate than requested. > Round up to avoid this. > > E.g. on Koelsch, the SPI flash (configured for 30 MHz) was driven at 48.75 > MHz. After this patch it's driven at a safe 24.375 MHz. > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> > --- > Simon: I think you want this in renesas-backports. Thanks, I'll backport it once its been accepted by Mark. > drivers/spi/spi-rspi.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c > index 1fb0ad213324..5639f9529e0b 100644 > --- a/drivers/spi/spi-rspi.c > +++ b/drivers/spi/spi-rspi.c > @@ -266,7 +266,8 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size) > rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); > > /* Sets transfer bit rate */ > - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1; > + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), > + 2 * rspi->max_speed_hz) - 1; > rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); > > /* Disable dummy transmission, set 16-bit word access, 1 frame */ > @@ -302,7 +303,8 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) > rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); > > /* Sets transfer bit rate */ > - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1; > + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), > + 2 * rspi->max_speed_hz) - 1; > rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); > > /* Disable dummy transmission, set byte access */ > @@ -335,7 +337,7 @@ static int qspi_set_config_register(struct rspi_data *rspi, int access_size) > rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); > > /* Sets transfer bit rate */ > - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz); > + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->max_speed_hz); > rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); > > /* Disable dummy transmission, set byte access */ > -- > 1.9.1 > -- To unsubscribe from this list: send the line "unsubscribe linux-spi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Thu, May 22, 2014 at 08:07:35PM +0200, Geert Uytterhoeven wrote: > The calculation of the bit rate divider used a standard C division, which > rounds down the quotient. This may lead to a higher bitrate than requested. > Round up to avoid this. Applied, thanks.
diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c index 1fb0ad213324..5639f9529e0b 100644 --- a/drivers/spi/spi-rspi.c +++ b/drivers/spi/spi-rspi.c @@ -266,7 +266,8 @@ static int rspi_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); /* Sets transfer bit rate */ - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1; + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), + 2 * rspi->max_speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); /* Disable dummy transmission, set 16-bit word access, 1 frame */ @@ -302,7 +303,8 @@ static int rspi_rz_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); /* Sets transfer bit rate */ - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz) - 1; + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), + 2 * rspi->max_speed_hz) - 1; rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); /* Disable dummy transmission, set byte access */ @@ -335,7 +337,7 @@ static int qspi_set_config_register(struct rspi_data *rspi, int access_size) rspi_write8(rspi, rspi->sppcr, RSPI_SPPCR); /* Sets transfer bit rate */ - spbr = clk_get_rate(rspi->clk) / (2 * rspi->max_speed_hz); + spbr = DIV_ROUND_UP(clk_get_rate(rspi->clk), 2 * rspi->max_speed_hz); rspi_write8(rspi, clamp(spbr, 0, 255), RSPI_SPBR); /* Disable dummy transmission, set byte access */
The calculation of the bit rate divider used a standard C division, which rounds down the quotient. This may lead to a higher bitrate than requested. Round up to avoid this. E.g. on Koelsch, the SPI flash (configured for 30 MHz) was driven at 48.75 MHz. After this patch it's driven at a safe 24.375 MHz. Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> --- Simon: I think you want this in renesas-backports. drivers/spi/spi-rspi.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)