Re: [PATCH v2 2/4] spi: s3c64xx: add cpu_relax in polling loop

[Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>]

On 19/04/2023 08:06, Jaewon Kim wrote:
> Adds cpu_relax() to prevent long busy-wait.

How cpu_relax prevents long waiting?

> There is busy-wait loop to check data transfer completion in polling mode.
> 
> Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
> ---
>  drivers/spi/spi-s3c64xx.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
> index 273aa02322d9..886722fb40ea 100644
> --- a/drivers/spi/spi-s3c64xx.c
> +++ b/drivers/spi/spi-s3c64xx.c
> @@ -568,6 +568,7 @@ static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
>  
>  	val = msecs_to_loops(ms);
>  	do {
> +		cpu_relax();

Shouldn't this be just readl_poll_timeout()? Or the syntax would be too
complicated?

>  		status = readl(regs + S3C64XX_SPI_STATUS);
>  	} while (RX_FIFO_LVL(status, sdd) < xfer->len && --val);
>  

Best regards,
Krzysztof