Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <b91c6cfb-4fd2-1189-72fd-92b40d1b4743@linaro.org>
Date:   Wed, 19 Apr 2023 10:19:54 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.10.0
Subject: Re: [PATCH v2 3/4] spi: s3c64xx: add sleep during transfer
Content-Language: en-US
To:     Jaewon Kim <jaewon02.kim@samsung.com>,
        Mark Brown <broonie@kernel.org>, Andi Shyti <andi@etezian.org>,
        Alim Akhtar <alim.akhtar@samsung.com>
Cc:     linux-spi@vger.kernel.org, linux-samsung-soc@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Chanho Park <chanho61.park@samsung.com>
References: <20230419060639.38853-1-jaewon02.kim@samsung.com>
 <CGME20230419062755epcas2p1bca14bbd5200ebe5241780d2d7ec1596@epcas2p1.samsung.com>
 <20230419060639.38853-4-jaewon02.kim@samsung.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
In-Reply-To: <20230419060639.38853-4-jaewon02.kim@samsung.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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@samsung.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);
> +	}

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