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

[Jaewon Kim]

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 at samsung.com>
---
 drivers/spi/spi-s3c64xx.c | 8 ++++++++
 1 file changed, 8 insertions(+)

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;
-- 
2.17.1