Unverified Commit 3456674f authored by Jaewon Kim's avatar Jaewon Kim Committed by Mark Brown
Browse files

spi: s3c64xx: add sleep during transfer 



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: default avatarJaewon Kim <jaewon02.kim@samsung.com>
Reviewed-by: default avatarKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20230502062813.112434-3-jaewon02.kim@samsung.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent d1a7718e

drivers/spi/spi-s3c64xx.c

+9 −2
Original line number Diff line number Diff line
@@ -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);