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Tue, 16 Apr 2019 16:59:07 +0900 (KST) Received: from epsmtrp2.samsung.com (unknown [182.195.40.14]) by epcas1p4.samsung.com (KnoxPortal) with ESMTPA id 20190416075907epcas1p42dc7016b49e3301f595f008fbafe43d6~V5XdjxEG_0271602716epcas1p4_; Tue, 16 Apr 2019 07:59:07 +0000 (GMT) Received: from epsmgms1p2new.samsung.com (unknown [182.195.42.42]) by epsmtrp2.samsung.com (KnoxPortal) with ESMTP id 20190416075907epsmtrp220e0b81939fbbac585e524ee9c3bf8e7~V5XdjDbCj2309323093epsmtrp2b; Tue, 16 Apr 2019 07:59:07 +0000 (GMT) X-AuditID: b6c32a35-98bff7000000102b-d0-5cb58b4b0ee0 Received: from epsmtip2.samsung.com ( [182.195.34.31]) by epsmgms1p2new.samsung.com (Symantec Messaging Gateway) with SMTP id 35.51.03662.B4B85BC5; Tue, 16 Apr 2019 16:59:07 +0900 (KST) Received: from [10.113.221.102] (unknown [10.113.221.102]) by epsmtip2.samsung.com (KnoxPortal) with ESMTPA id 20190416075907epsmtip2777303bc256b707804fc4ea6bf6f69a0~V5XdVdIH52964229642epsmtip2a; Tue, 16 Apr 2019 07:59:07 +0000 (GMT) Subject: Re: [PATCH v2 05/19] PM / devfreq: tegra: Replace write memory barrier with the read barrier To: Dmitry Osipenko , Thierry Reding , Jonathan Hunter , MyungJoo Ham , Kyungmin Park , Tomeu Vizoso Cc: linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org From: Chanwoo Choi Organization: Samsung Electronics Message-ID: Date: Tue, 16 Apr 2019 17:00:01 +0900 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190415145505.18397-6-digetx@gmail.com> Content-Language: en-US Content-Transfer-Encoding: 8bit X-Brightmail-Tracker: H4sIAAAAAAAAA01SWUwTURT1dZlO0epYBK+NURiXCLGUoRYGA4pCtAYTif6okOBIx0LoZqcl rgkqKlRxj0vdRRJFTUktiBXSgLgLIaCCEsQENK4QQI3GhNh2auTvvHvOfeee9y4ulFdjCrzA ZGOtJsZAYmGi2vsxccrMAzU58cXVs+gbQ32ILnFeEdEtu79K6A7vOYweKW9GdNl3J0Z377qG 0b+9F0T0oVvtWJpUW9dzFWnvOnsk2vI9A5j2kKcKaUfcM7LE6wtT8llGx1qjWFOeWVdg0qeS mWty03M1ifGUkkqmk8goE2NkU8mMlVnKZQUG/0BkVBFjsPtLWQzHkapFKVaz3cZG5Zs5WyrJ WnQGS7IljmOMnN2kj8szGxdS8fEJGr9wQ2F+1ZAPs7wYv6XrfIewGPmkDiTFgVgAnXc6BQ4U hsuJOgQPPL1YgJATwwhuetN44ieCly9GRP86XvdcCXU0IGhzVoYOgwh+ffKJA6pwQg+OU/fE AWIKMYpg2Hs6SAiJdfCjsVIYwBgRC76PXUG/SUQ0vPzVhwJYRiyCw6OngnoRMQcuux1BHEGs hd6H1WJeMxmenOkPjiQlEqHl1TcBf/9UeNN/MYRnwp6as8LAEED8weDk+2IJnyED2ve+RTwO h8+PPKG6AkYGGjAeb4frT5oxvrkUgcfXJuYJNfgqj/sdcL9DDLi8Kt5sIgz8OCgOlIGQQek+ Oa+eBR3vegQ8ngYV+8tC12uh3jUqOYKinWPiOMdEcI6J4PxvdgmJqlAka+GMepajLNTY73aj 4LbGaurQidaVTYjAETlBhh/05MjFTBG31diEABeSU2RLdP6STMds3cZazblWu4HlmpDG/9pH hYqIPLN/9022XEqToFar6QVUooaiyKkyV1p6jpzQMza2kGUtrPVfnwCXKopRxQWH6t7qxaXQ r36caWqtH+wTzI/uRHPnlVhWZJ5PUrpKl/2ZWDXnw61sxdIaV1H5o3O1dsk4jfvYqqEdFQmc AreW3f8im/4+KXs4fTMeGfY0RVkhmxRBVUZu7B0tYSardg7GNBbVL29w3/65vHlzxrPuDbM/ 70LJyaLnNdfKVJtIEZfPULFCK8f8BU8Lx4HDAwAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFprNIsWRmVeSWpSXmKPExsWy7bCSvK5399YYg+75nBarPz5mtGiZtYjF 4mzTG3aLy7vmsFl87j3CaNH5ZRabxe3GFWwWP3fNY7HoW3uJzYHTY8fdJYweO2fdZffobX7H 5tG3ZRWjx+dNcgGsUVw2Kak5mWWpRfp2CVwZqz7uZyu4wl1xY+5l5gbG/ZxdjJwcEgImEjfv LmLqYuTiEBLYzShx+uZ5JoiEpMS0i0eZuxg5gGxhicOHiyFq3jJKrGrZyAxSIyyQLtE1fTcr SEJEoIlJ4vPDFrBmZoFIif5H3awQHVsZJfp+n2IFSbAJaEnsf3GDDcTmF1CUuPrjMSOIzStg J9H/bzpYDYuAqsTCTV1gtqhAhMSZ9ytYIGoEJU7OfAJmcwqYSZy99hZqmbrEn3mXmCFscYlb T+ZDxeUlmrfOZp7AKDwLSfssJC2zkLTMQtKygJFlFaNkakFxbnpusWGBUV5quV5xYm5xaV66 XnJ+7iZGcJRpae1gPHEi/hCjAAejEg9vQt+WGCHWxLLiytxDjBIczEoivI4pQCHelMTKqtSi /Pii0pzU4kOM0hwsSuK88vnHIoUE0hNLUrNTUwtSi2CyTBycUg2MEg+TI3NtDn9mamGu1Jg+ 0XJL7KrVqRdWPvLZujyGaTHPsR8SyUp9k1fdiljCGNfa7D1XIP7KFO7HjfIBxg9/itfcqVjB 3Zj+Mzeg6ZW3w/be7Ven+1mlM+U/exiT81R8wyJx5so17Hkp95n2sVX1evx8lLrq0IE7f1q1 E9w0dJ1dT3pP2C2lxFKckWioxVxUnAgAjfk3C64CAAA= X-CMS-MailID: 20190416075907epcas1p42dc7016b49e3301f595f008fbafe43d6 X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" CMS-TYPE: 101P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20190415145805epcas1p209d0e2a8ba052ad11e91155c4585b1bd References: <20190415145505.18397-1-digetx@gmail.com> <20190415145505.18397-6-digetx@gmail.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 19. 4. 15. 오후 11:54, Dmitry Osipenko wrote: > The write memory barrier isn't needed because the BUS buffer is flushed > by read after write that happens after the removed wmb(), we will also > use readl() instead of the relaxed version to ensure that read is indeed > completed. > > Signed-off-by: Dmitry Osipenko > --- > drivers/devfreq/tegra-devfreq.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/drivers/devfreq/tegra-devfreq.c b/drivers/devfreq/tegra-devfreq.c > index d62fb1b0d9bb..f0f0d78f6cbf 100644 > --- a/drivers/devfreq/tegra-devfreq.c > +++ b/drivers/devfreq/tegra-devfreq.c > @@ -243,8 +243,7 @@ static void tegra_devfreq_update_wmark(struct tegra_devfreq *tegra, > static void actmon_write_barrier(struct tegra_devfreq *tegra) > { > /* ensure the update has reached the ACTMON */ > - wmb(); > - actmon_readl(tegra, ACTMON_GLB_STATUS); > + readl(tegra->regs + ACTMON_GLB_STATUS); I think that this meaning of actmon_write_barrier() keeps the order of 'store' assembly command without the execution change from compiler optimization by using the wmb(). But, this patch edits it as following: The result of the following two cases are same? [original code] wmb() read_relaxed() [new code by this patch] readl_relaxed() rmb() > } > > static void actmon_isr_device(struct tegra_devfreq *tegra, > -- Best Regards, Chanwoo Choi Samsung Electronics