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

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Date:   Wed, 19 Apr 2023 15:06:38 +0900
From:   Jaewon Kim <jaewon02.kim@...sung.com>
To:     Mark Brown <broonie@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andi Shyti <andi@...zian.org>,
        Alim Akhtar <alim.akhtar@...sung.com>
Cc:     linux-spi@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Chanho Park <chanho61.park@...sung.com>,
        Jaewon Kim <jaewon02.kim@...sung.com>
Subject: [PATCH v2 3/4] spi: s3c64xx: add sleep during transfer

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@...sung.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