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

[Krzysztof Kozlowski]

On 19/04/2023 08:06, Jaewon Kim wrote:
> 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@xxxxxxxxxxx>
> ---
>  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);
> +	}

Did you actually check the delays introduced by it? Is it worth?

>  
>  	/* millisecs to xfer 'len' bytes @ 'cur_speed' */
>  	ms = xfer->len * 8 * 1000 / sdd->cur_speed;

You have now some code duplication so this could be combined.

Best regards,
Krzysztof