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[68.147.8.254]) by smtp.gmail.com with ESMTPSA id d19sm2995373pjs.22.2019.06.18.15.34.03 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 18 Jun 2019 15:34:04 -0700 (PDT) Date: Tue, 18 Jun 2019 16:34:02 -0600 From: Mathieu Poirier To: Andrew Murray Subject: Re: [PATCH v1 2/5] coresight: etm4x: use explicit barriers on enable/disable Message-ID: <20190618223402.GA24894@xps15> References: <20190618125433.9739-1-andrew.murray@arm.com> <20190618125433.9739-3-andrew.murray@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190618125433.9739-3-andrew.murray@arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190618_153405_668034_1DF112F2 X-CRM114-Status: GOOD ( 18.75 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alexander Shishkin , linux-arm-kernel@lists.infradead.org, Suzuki K Poulose Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jun 18, 2019 at 01:54:30PM +0100, Andrew Murray wrote: > Synchronization is recommended before disabling the trace registers > to prevent any start or stop points being speculative at the point > of disabling the unit (section 7.3.77 of ARM IHI 0064D). > > Synchronization is also recommended after programming the trace > registers to ensure all updates are committed prior to normal code > resuming (section 4.3.7 of ARM IHI 0064D). > > Let's ensure these syncronization points are present in the code > and clearly commented. > > Note that we could rely on the barriers in CS_LOCK and > coresight_disclaim_device_unlocked or the context switch to user > space - however coresight may be of use in the kernel. > > Signed-off-by: Andrew Murray > --- > drivers/hwtracing/coresight/coresight-etm4x.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x.c > index da7cf74d612b..ae623415c431 100644 > --- a/drivers/hwtracing/coresight/coresight-etm4x.c > +++ b/drivers/hwtracing/coresight/coresight-etm4x.c > @@ -187,6 +187,10 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata) > dev_err(drvdata->dev, > "timeout while waiting for Idle Trace Status\n"); > > + /* As recommended by 4.3.7 of ARM IHI 0064D */ > + dsb(sy); > + isb(); > + > done: > CS_LOCK(drvdata->base); > > @@ -453,7 +457,8 @@ static void etm4_disable_hw(void *info) > control &= ~0x1; > > /* make sure everything completes before disabling */ > - mb(); > + /* As recommended by 7.3.77 of ARM IHI 0064D */ > + dsb(sy); As far as I can tell mb() is equal to dsb(sy). > isb(); > writel_relaxed(control, drvdata->base + TRCPRGCTLR); > > -- > 2.21.0 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel