[PATCH v3 2/3] spi: s3c64xx: add sleep during transfer

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



In polling mode, the status register is continuously read to check data
transfer completion. It can cause excessive CPU usage.
To reduce this, we can calculate the transfer time and put the sleep during
transfer.

When test on ExynosAuto9 SADK board, throughput remained the same, but
100% CPU utilization decreased to 40%.

Signed-off-by: Jaewon Kim <jaewon02.kim@xxxxxxxxxxx>
---
 drivers/spi/spi-s3c64xx.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 66ac94022a1b..2a8304678df9 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -561,11 +561,18 @@ static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
 	u32 cpy_len;
 	u8 *buf;
 	int ms;
+	unsigned long time_us;
 
-	/* millisecs to xfer 'len' bytes @ 'cur_speed' */
-	ms = xfer->len * 8 * 1000 / sdd->cur_speed;
+	/* microsecs to xfer 'len' bytes @ 'cur_speed' */
+	time_us = (xfer->len * 8 * 1000 * 1000) / sdd->cur_speed;
+	ms = (time_us / 1000);
 	ms += 10; /* some tolerance */
 
+	/* sleep during signal transfer time */
+	status = readl(regs + S3C64XX_SPI_STATUS);
+	if (RX_FIFO_LVL(status, sdd) < xfer->len)
+		usleep_range(time_us / 2, time_us);
+
 	val = msecs_to_loops(ms);
 	do {
 		status = readl(regs + S3C64XX_SPI_STATUS);
-- 
2.17.1




[Index of Archives]     [Linux Kernel]     [Linux ARM (vger)]     [Linux ARM MSM]     [Linux Omap]     [Linux Arm]     [Linux Tegra]     [Fedora ARM]     [Linux for Samsung SOC]     [eCos]     [Linux Fastboot]     [Gcc Help]     [Git]     [DCCP]     [IETF Announce]     [Security]     [Linux MIPS]     [Yosemite Campsites]

  Powered by Linux