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([2a02:810d:15c0:828:62f5:eb43:f726:5fee]) by smtp.gmail.com with ESMTPSA id q1-20020aa7d441000000b0050499afe96bsm7880909edr.10.2023.04.19.01.19.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Apr 2023 01:19:55 -0700 (PDT) Message-ID: 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 , Mark Brown , Andi Shyti , Alim Akhtar 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 References: <20230419060639.38853-1-jaewon02.kim@samsung.com> <20230419060639.38853-4-jaewon02.kim@samsung.com> From: Krzysztof Kozlowski In-Reply-To: <20230419060639.38853-4-jaewon02.kim@samsung.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > --- > 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