From 3456674f54d3cfdedb28ce8a3db2b6f975392ac8 Mon Sep 17 00:00:00 2001
From: Jaewon Kim <jaewon02.kim@samsung.com>
Date: Tue, 2 May 2023 15:28:12 +0900
Subject: 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: Jaewon Kim <jaewon02.kim@samsung.com
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org
Link: https://lore.kernel.org/r/20230502062813.112434-3-jaewon02.kim@samsung.com
Signed-off-by: Mark Brown <broonie@kernel.org
---
 drivers/spi/spi-s3c64xx.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

(limited to 'drivers/spi/spi-s3c64xx.c')

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 5f59d6f8c8d8..38cc2068afce 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);
-- 
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