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[v2,3/4] spi: s3c64xx: add sleep during transfer

Message ID 20230419060639.38853-4-jaewon02.kim@samsung.com
State New
Headers show
Series Improves polling mode of s3c64xx driver | expand

Commit Message

Jaewon Kim April 19, 2023, 6:06 a.m. UTC 
In polling mode, the status register is constantly read to check transfer
completion. It cause excessive CPU usage.
So, it calculates the SPI transfer time and made it sleep.

Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
---
 drivers/spi/spi-s3c64xx.c | 8 ++++++++
 1 file changed, 8 insertions(+)
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Patch

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index 886722fb40ea..cf3060b2639b 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -561,6 +561,14 @@  static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
 	u32 cpy_len;
 	u8 *buf;
 	int ms;
+	u32 tx_time;
+
+	/* sleep during signal transfer time */
+	status = readl(regs + S3C64XX_SPI_STATUS);
+	if (RX_FIFO_LVL(status, sdd) < xfer->len) {
+		tx_time = (xfer->len * 8 * 1000 * 1000) / sdd->cur_speed;
+		usleep_range(tx_time / 2, tx_time);
+	}
 
 	/* millisecs to xfer 'len' bytes @ 'cur_speed' */
 	ms = xfer->len * 8 * 1000 / sdd->cur_speed;