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authorTrent Piepho <tpiepho@gmail.com>2013-10-01 13:15:47 -0700
committerMark Brown <broonie@linaro.org>2013-10-18 01:00:32 +0100
commita560943ead2cbded93c30c9b04886f3c743d7f00 (patch)
tree5b585266e5d3660eb93b5fe2f6c4a80da3061a44
parentaa9e0c6feb3e06463b45b0d9734a2cdbf95c4431 (diff)
spi: spi-mxs: Don't set clock for each xfer
mxs_spi_setup_transfer() would set the SSP SCK rate every time it was called, which is before every transfer. It is uncommon for the SCK rate to change between transfers (or at all of that matter) and this causes many unnecessary reprogrammings of the clock registers. Code changed to only set the rate when it changes. This significantly speeds up short SPI messages, especially messages made up of many transfers, as the calculation of the clock divisors is rather costly. 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> Signed-off-by: Mark Brown <broonie@linaro.org>
-rw-r--r--drivers/spi/spi-mxs.c15
1 files changed, 14 insertions, 1 deletions
diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c
index 9e6101a38e85..759de701f050 100644
--- a/drivers/spi/spi-mxs.c
+++ b/drivers/spi/spi-mxs.c
@@ -67,6 +67,7 @@
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,
@@ -81,7 +82,19 @@ 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 rate, hz, rather than the actual rate,
+ * ssp->clk_rate. Otherwise we would set the rate every trasfer
+ * when the actual rate is not quite the same as requested rate.
+ */
+ 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);