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Fri, 21 Apr 2023 10:48:10 +0900 (KST) Received: from [10.229.8.168] (unknown [10.229.8.168]) by epsmtip1.samsung.com (KnoxPortal) with ESMTPA id 20230421014810epsmtip175cfaddfaea55304c37787c52014b006~X0AFpyRCk2749627496epsmtip1L; Fri, 21 Apr 2023 01:48:10 +0000 (GMT) Message-ID: <87c2a0e1-fb3a-7b0a-c87a-ac792357ef26@samsung.com> Date: Fri, 21 Apr 2023 10:45:45 +0900 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 2/4] spi: s3c64xx: add cpu_relax in polling loop Content-Language: en-US To: Krzysztof Kozlowski , 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 From: Jaewon Kim In-Reply-To: <01d22e48-40f0-b1dd-aa00-cf484c4364ee@linaro.org> X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrGJsWRmVeSWpSXmKPExsWy7bCmmW7Ua8cUg78nrS0ezNvGZrH4x3Mm i6kPn7BZXN6vbbH39VZ2i02Pr7FaXN41h81ixvl9TBaNH2+yO3B6XF/yidlj06pONo871/aw eWxeUu/Rt2UVo8fnTXIBbFHZNhmpiSmpRQqpecn5KZl56bZK3sHxzvGmZgaGuoaWFuZKCnmJ uam2Si4+AbpumTlANykplCXmlAKFAhKLi5X07WyK8ktLUhUy8otLbJVSC1JyCswL9IoTc4tL 89L18lJLrAwNDIxMgQoTsjNuv13HWrCOr+Js2w7WBsZz3F2MnBwSAiYSp7ZfZO9i5OIQEtjB KHFq5wlmCOcTo8TJGbsYIZzPjBJTd7YxwbT8eTyTDSKxi1Fiya6jUFWvGSW2v7/NAlLFK2An cfnHZUYQm0VAVeLXu92sEHFBiZMzn4DViApESyzeNwXMFhZwl9hx9R9YPbOAuMStJ/OZQIaK CCxmlOh7/AlsHbPARkaJzU1T2UGq2AS0Jb6vXww2lRNo281385ghuuUltr+dA/aFhMBcDolr y2YzQhzuInH9YAM7hC0s8er4FihbSuJlfxuUnS3RPv0PK4RdIXFxw2w2CNtYYtazdqA5HEAL NCXW79IHMSUElCWO3GKBWMsn0XH4LztEmFeio00IolFN4v7Uc1BDZCQmHVkJDUUPiSMzd7FN YFSchRQss5C8PwvJM7MQ9i5gZFnFKJZaUJybnlpsVGAIj+7k/NxNjOAEq+W6g3Hy2w96hxiZ OBgPMUpwMCuJ8J5xtUoR4k1JrKxKLcqPLyrNSS0+xGgKjJyJzFKiyfnAFJ9XEm9oYmlgYmZm aG5kamCuJM4rbXsyWUggPbEkNTs1tSC1CKaPiYNTqoEpcqHzr40379dtTu8Mn7j0ziP7zS5X lpoEMTtunrVeYLXTmdrSTZU6e9z9qk592DMrqe703suFHzY8+VV56/kzXTWtlQejr7RZ+Llf PaxU0save313TORicTnhNYZ5bF6eGStzMxot3qxeaFIp5/tte4RQYPcM5tcrLhtnWP5Z+Prg ijM2knJTqx7c3H60PO/iVLNm7nlHSu+dmfFKoOT7Bxl+3tcpbLfPC7QprlWVW3VVkzFrx7Fo 7YfRscVRVXf+XHF5VD6VaSdPutfueuPpSta6HQ/jqoSb5rvH8u3tPvHAqP6EoM0PM4OpHXvZ Cwz9VZnnzr1yOawya9LHY69i4/bohInaVYnb7T2/se2/EktxRqKhFnNRcSIAKEYrQTkEAAA= X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFmpnkeLIzCtJLcpLzFFi42LZdlhJTjfqtWOKwd27chYP5m1js1j84zmT xdSHT9gsLu/Xttj7eiu7xabH11gtLu+aw2Yx4/w+JovGjzfZHTg9ri/5xOyxaVUnm8eda3vY PDYvqffo27KK0ePzJrkAtigum5TUnMyy1CJ9uwSujNtv17EWrOOrONu2g7WB8Rx3FyMnh4SA icSfxzPZuhi5OIQEdjBKPJ/VwgSRkJFY/qyPDcIWlrjfcoQVouglo8T0r1NYQRK8AnYSl39c ZgSxWQRUJX692w0VF5Q4OfMJC4gtKhAtcWP5N7ChwgLuEjuu/gOrZxYQl7j1ZD4TyFARgcWM Eh2X3rKDOMwCGxklVl5fzwyx7hGTxONJN8HGsgloS3xfvxjM5gRaffPdPGaIUWYSXVu7oMbK S2x/O4d5AqPQLCSXzEKycRaSlllIWhYwsqxilEwtKM5Nzy02LDDKSy3XK07MLS7NS9dLzs/d xAiOKy2tHYx7Vn3QO8TIxMF4iFGCg1lJhPeMq1WKEG9KYmVValF+fFFpTmrxIUZpDhYlcd4L XSfjhQTSE0tSs1NTC1KLYLJMHJxSDUxJRytPni+bzTX7aVLOnt3qAp9nPjE/xDxpfaZlyo/+ 6Z7XDvqdemP9mlnba3Gyou+mvTFbUz3LTycVpHxSeKR+fFLUlNDiNJsF0tvPL8/gsloh1Tq1 da/R2WfMYXZCeQcucCy49j42wSu0RcH+umqjbXmIEYcvlwff/2w+uSXvJWT6nm/e+3nFqsiz S4r6p0ouC1+qwzbhkd3y7jIFnrKZu3ddaDDiaHsiyHlHN+1C0ul45+Dsh8yvyrjrToauPLNL ffL5FAujKsFdd3Itj2aIyD13OZLxTCTg9TFrkarQK9FzuzIt69kmT5u/4kfzdp+XcZsveage u5ptzrI53bn1cXBhV4Kae7hFR8KSCiWW4oxEQy3mouJEALwSynwaAwAA X-CMS-MailID: 20230421014810epcas2p1712c2740eac5eaa34006237858dfd8e5 X-Msg-Generator: CA X-Sendblock-Type: AUTO_CONFIDENTIAL CMS-TYPE: 102P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20230419062755epcas2p43a646bbae5f01e3120331407ad873318 References: <20230419060639.38853-1-jaewon02.kim@samsung.com> <20230419060639.38853-3-jaewon02.kim@samsung.com> <36f37a18-0022-0368-bf7c-ebdd724b1558@linaro.org> <01d22e48-40f0-b1dd-aa00-cf484c4364ee@linaro.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230420_184814_682491_1535C39F X-CRM114-Status: GOOD ( 23.56 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 23. 4. 21. 00:39, Krzysztof Kozlowski wrote: > On 19/04/2023 13:13, Jaewon Kim wrote: >> On 23. 4. 19. 17:14, Krzysztof Kozlowski wrote: >>> On 19/04/2023 08:06, Jaewon Kim wrote: >>>> Adds cpu_relax() to prevent long busy-wait. >>> How cpu_relax prevents long waiting? >> As I know, cpu_relax() can be converted to yield. This can prevent >> excessive use of the CPU in busy-loop. > That's ok, you just wrote that it will prevent long waiting, so I assume > it will shorten the wait time. > >> I'll replace poor sentence like below in v3. >> >> ("Adds cpu_relax() to allow CPU relaxation in busy-loop") >> >>>> There is busy-wait loop to check data transfer completion in polling mode. >>>> >>>> Signed-off-by: Jaewon Kim >>>> --- >>>> 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? >> I think we can replace this while() loop to readl_poll_timeout(). >> >> However, we should use 0 value as 'delay_us' parameter. Because delay >> can affect throughput. >> >> >> My purpose is add relax to this busy-loop. >> >> we cannot give relax if we change to readl_poll_timeout(). > readl_poll_timeout() will know to do the best. You do not need to add > cpu_relax there. Okay, I will change it to readl_poll_timeout() > > Best regards, > Krzysztof > > Thanks Jaewon Kim _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel