linux-kernel - Re: [PATCH v2 2/4] spi: s3c64xx: add cpu

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Date:   Wed, 19 Apr 2023 10:14:01 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jaewon Kim <jaewon02.kim@...sung.com>,
        Mark Brown <broonie@...nel.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>
Subject: Re: [PATCH v2 2/4] spi: s3c64xx: add cpu_relax in polling loop

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@...sung.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