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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
This commit is contained in:
Jaewon Kim 2023-05-02 15:28:12 +09:00 committed by Mark Brown
parent d1a7718ee8
commit 3456674f54
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GPG Key ID: 24D68B725D5487D0
1 changed files with 9 additions and 2 deletions
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11
drivers/spi/spi-s3c64xx.c
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@ -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);