Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   Suzuki K Poulose <suzuki.poulose@arm.com>
To:     linux-arm-kernel@lists.infradead.org
Cc:     coresight@lists.linaro.org, mathieu.poirier@linaro.org,
        anshuman.khandual@arm.com, mike.leach@linaro.org,
        leo.yan@linaro.org, linux-kernel@vger.kernel.org,
        jonathan.zhouwen@huawei.com, catalin.marinas@arm.com,
        Suzuki K Poulose <suzuki.poulose@arm.com>
Subject: [PATCH v7 21/28] coresight: etm4x: Add necessary synchronization for sysreg access
Date:   Sun, 10 Jan 2021 22:48:43 +0000
Message-Id: <20210110224850.1880240-22-suzuki.poulose@arm.com>
In-Reply-To: <20210110224850.1880240-1-suzuki.poulose@arm.com>
References: <20210110224850.1880240-1-suzuki.poulose@arm.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

As per the specification any update to the TRCPRGCTLR must be synchronized
by a context synchronization event (in our case an explicist ISB) before
the TRCSTATR is checked.

Cc: Mike Leach <mike.leach@linaro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
---
 drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 5d3041eccc14..3b17feb86d8a 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -284,6 +284,15 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 	/* Disable the trace unit before programming trace registers */
 	etm4x_relaxed_write32(csa, 0, TRCPRGCTLR);
 
+	/*
+	 * If we use system instructions, we need to synchronize the
+	 * write to the TRCPRGCTLR, before accessing the TRCSTATR.
+	 * See ARM IHI0064F, section
+	 * "4.3.7 Synchronization of register updates"
+	 */
+	if (!csa->io_mem)
+		isb();
+
 	/* wait for TRCSTATR.IDLE to go up */
 	if (coresight_timeout(csa, TRCSTATR, TRCSTATR_IDLE_BIT, 1))
 		dev_err(etm_dev,
@@ -362,6 +371,10 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
 	/* Enable the trace unit */
 	etm4x_relaxed_write32(csa, 1, TRCPRGCTLR);
 
+	/* Synchronize the register updates for sysreg access */
+	if (!csa->io_mem)
+		isb();
+
 	/* wait for TRCSTATR.IDLE to go back down to '0' */
 	if (coresight_timeout(csa, TRCSTATR, TRCSTATR_IDLE_BIT, 0))
 		dev_err(etm_dev,
-- 
2.24.1