| Message ID | 1364905195-24286-11-git-send-email-tpiepho@gmail.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
Dear Trent Piepho, > mxs_spi_setup_transfer() would set the SSP SCK rate every time it was > called, which is before each transfer. It is uncommon for the SCK rate to > change between transfers and this causes unnecessary reprogramming of the > clock registers. Changed to only set the rate when it has changed. > > This significantly speeds up short SPI messages, especially messages made > up of many transfers. On an iMX287, using spidev with messages that > consist of 511 transfers of 4 bytes each at an SCK of 48 MHz, the > effective transfer rate more than doubles from about 290 KB/sec to 600 > KB/sec. > > Signed-off-by: Trent Piepho <tpiepho@gmail.com> > Cc: Marek Vasut <marex@denx.de> > Cc: Fabio Estevam <fabio.estevam@freescale.com> > Cc: Shawn Guo <shawn.guo@linaro.org> > --- > drivers/spi/spi-mxs.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c > index a7d5f85..12794ea 100644 > --- a/drivers/spi/spi-mxs.c > +++ b/drivers/spi/spi-mxs.c > @@ -68,6 +68,7 @@ > struct mxs_spi { > struct mxs_ssp ssp; > struct completion c; Stick the comment here. > + unsigned int sck; /* Rate requested (vs actual) */ > }; > > static int mxs_spi_setup_transfer(struct spi_device *dev, > @@ -88,7 +89,19 @@ static int mxs_spi_setup_transfer(struct spi_device > *dev, return -EINVAL; > } > > - mxs_ssp_set_clk_rate(ssp, hz); > + if (hz != spi->sck) { > + mxs_ssp_set_clk_rate(ssp, hz); > + /* > + * Save requested value, not actual value from ssp->clk_rate. > + * Otherwise we would set the rate again each trasfer when > + * actual is not quite the same as requested. > + */ > + spi->sck = hz; > + /* > + * Perhaps we should return an error if the actual clock is > + * nowhere close to what was requested? > + */ Maybe you want to check the ssp->ssp_clk vs. hz indeed. > + } > > writel(BM_SSP_CTRL0_LOCK_CS, > ssp->base + HW_SSP_CTRL0 + STMP_OFFSET_REG_SET); Best regards, Marek Vasut ------------------------------------------------------------------------------ Minimize network downtime and maximize team effectiveness. Reduce network management and security costs.Learn how to hire the most talented Cisco Certified professionals. Visit the Employer Resources Portal http://www.cisco.com/web/learning/employer_resources/index.html
diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c index a7d5f85..12794ea 100644 --- a/drivers/spi/spi-mxs.c +++ b/drivers/spi/spi-mxs.c @@ -68,6 +68,7 @@ struct mxs_spi { struct mxs_ssp ssp; struct completion c; + unsigned int sck; /* Rate requested (vs actual) */ }; static int mxs_spi_setup_transfer(struct spi_device *dev, @@ -88,7 +89,19 @@ static int mxs_spi_setup_transfer(struct spi_device *dev, return -EINVAL; } - mxs_ssp_set_clk_rate(ssp, hz); + if (hz != spi->sck) { + mxs_ssp_set_clk_rate(ssp, hz); + /* + * Save requested value, not actual value from ssp->clk_rate. + * Otherwise we would set the rate again each trasfer when + * actual is not quite the same as requested. + */ + spi->sck = hz; + /* + * Perhaps we should return an error if the actual clock is + * nowhere close to what was requested? + */ + } writel(BM_SSP_CTRL0_LOCK_CS, ssp->base + HW_SSP_CTRL0 + STMP_OFFSET_REG_SET);
mxs_spi_setup_transfer() would set the SSP SCK rate every time it was called, which is before each transfer. It is uncommon for the SCK rate to change between transfers and this causes unnecessary reprogramming of the clock registers. Changed to only set the rate when it has changed. This significantly speeds up short SPI messages, especially messages made up of many transfers. On an iMX287, using spidev with messages that consist of 511 transfers of 4 bytes each at an SCK of 48 MHz, the effective transfer rate more than doubles from about 290 KB/sec to 600 KB/sec. Signed-off-by: Trent Piepho <tpiepho@gmail.com> Cc: Marek Vasut <marex@denx.de> Cc: Fabio Estevam <fabio.estevam@freescale.com> Cc: Shawn Guo <shawn.guo@linaro.org> --- drivers/spi/spi-mxs.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)