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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 From: Jaewon Kim Subject: Re: [PATCH v2 2/4] spi: s3c64xx: add cpu_relax in polling loop 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 Content-Language: en-US In-Reply-To: <36f37a18-0022-0368-bf7c-ebdd724b1558@linaro.org> Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrKJsWRmVeSWpSXmKPExsWy7bCmqW7mWfsUgwWtJhYP5m1js1j84zmT xdSHT9gsLu/Xttj7eiu7xabH11gtLu+aw2Yx4/w+JovGjzfZHTg9ri/5xOyxaVUnm8eda3vY PDYvqffo27KK0ePzJrkAtqhsm4zUxJTUIoXUvOT8lMy8dFsl7+B453hTMwNDXUNLC3MlhbzE 3FRbJRefAF23zBygm5QUyhJzSoFCAYnFxUr6djZF+aUlqQoZ+cUltkqpBSk5BeYFesWJucWl eel6eaklVoYGBkamQIUJ2RkLX91mL/jLXXFj/iHWBsaznF2MnBwSAiYSL149Z+ti5OIQEtjB KLF+zQlWCOcTo0TTn31MEM43RomeW6dYYFq2nnnJApHYyyixZeUWRgjnNaPEnlkn2LsYOTh4 BewkLixgBmlgEVCVuDp/PTuIzSsgKHFy5hOwQaIC0RKL900Bs9kEtCW+r1/MCmILC7hL7Lj6 D2ymiMBiRom+x5/ADmQW2MgosblpKtgkZgFxiVtP5jOB2JxAyzrWXGGCiMtLbH87hxmkQUJg KYfE9KdrGCHudpG4sPopG4QtLPHq+BZ2CFtK4mV/G5SdLdE+/Q8rhF0hcXHDbKh6Y4lZz9oZ QT5jFtCUWL9LH8SUEFCWOHKLBWItn0TH4b/sEGFeiY42IYhGNYn7U89BDZGRmHRkJROE7SFx ZOYutgmMirOQgmUWksdmIXlmFsLeBYwsqxjFUguKc9NTi40KjOGxnZyfu4kRnF613Hcwznj7 Qe8QIxMH4yFGCQ5mJRHeM65WKUK8KYmVValF+fFFpTmpxYcYTYGRM5FZSjQ5H5jg80riDU0s DUzMzAzNjUwNzJXEeaVtTyYLCaQnlqRmp6YWpBbB9DFxcEo1MCU+FZ2pce9McuOBsMQvL+y0 y0TiD76eoftjU/9MS/6AQq8+58vNgmG7vloeLQps33fZ6ePRJblTeGepTHeOeCvvsHbB5DiB N9lr3HKnp7i2n2Atkpiy5VDBwlVbsittuG5M28q44Bfb69YPOvrHig7Znfr9hn3tEeWP5mvn 7TBmZk5RfdG6v6LXM3YNY56u3N05SmF8Ub4xCU1r150RP/W76/d3DpuQv7+utfMtWsVye0Fq qPbrd/UcKv8lLhR8+xPiLiPRVbPsQOGzJPX1rnGWlimq+4SiZ3HpvpU9l3LgZv42/baCN+tf Luiwv1F7edkrhq1sazJXh5splre9S9vxq2aVGNurssehU5gyNiixFGckGmoxFxUnAgCRebcX OAQAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFmplkeLIzCtJLcpLzFFi42LZdlhJTjfzrH2Kwc1N/BYP5m1js1j84zmT xdSHT9gsLu/Xttj7eiu7xabH11gtLu+aw2Yx4/w+JovGjzfZHTg9ri/5xOyxaVUnm8eda3vY PDYvqffo27KK0ePzJrkAtigum5TUnMyy1CJ9uwSujIWvbrMX/OWuuDH/EGsD41nOLkZODgkB E4mtZ16ydDFycQgJ7GaU+NU6gQUiISOx/FkfG4QtLHG/5QgrRNFLRon/B78CFXFw8ArYSVxY wAxSwyKgKnF1/np2EJtXQFDi5MwnYHNEBaIlbiz/xgRiswloS3xfv5gVxBYWcJfYcfUfI8hM EYHFjBIdl96ygzjMAhsZJVZeXw82VUjgJ6PEpslSIDazgLjErSfzwSZxAi3uWHOFCSJuJtG1 tYsRwpaX2P52DvMERqFZSA6ZhaR9FpKWWUhaFjCyrGKUTC0ozk3PLTYsMMxLLdcrTswtLs1L 10vOz93ECI4pLc0djNtXfdA7xMjEwXiIUYKDWUmE193GLkWINyWxsiq1KD++qDQntfgQozQH i5I474Wuk/FCAumJJanZqakFqUUwWSYOTqkGJlvPZZfns54M2qPw+1X19ZcevRUc0qKTBOwN pvSf3PPMcl4ZC4Ppultf/+43slPNuv3i/ry1i4TT9PwLnDWzpe7fPC1xqWFG9LIjL08FP0zZ Y6FxY+FK84w3/8ydMtv8Z0aILRNz8tOZmPboSe/vzkd72EuMizsuSkx3Y647nPeoL2Tq9SMr 3fOrrNO8D157syR38stX8tObs1qW7uzKFalfscPn/Vm/JzKVLB3/zhkf2F5+YMbL25lWzYfr li1RSbFfJqSqZCn+7VmIXf02dj++efmabd5H0yR5xRfkij5RFT6yVyWeL+zK12eZlpsZfnSw zpCfeet5VAPj9eq55xequH0L1ZpRf9xns9GpCCWW4oxEQy3mouJEADgrUgIYAwAA X-CMS-MailID: 20230419111553epcas2p34439437568e4ab428e9464f41889eb33 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" 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> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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(). >> status = readl(regs + S3C64XX_SPI_STATUS); >> } while (RX_FIFO_LVL(status, sdd) < xfer->len && --val); >> > Best regards, > Krzysztof > > Thanks Jaewon Kim