linux-kernel - [PATCH v5 19/25] coresight: etm4x: Add necessary synchronization for sysreg access

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Message-Id: <20201214173731.302520-20-suzuki.poulose@arm.com>
Date:   Mon, 14 Dec 2020 17:37:25 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, catalin.marinas@....com,
        mathieu.poirier@...aro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, jonathan.zhouwen@...wei.com,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v5 19/25] coresight: etm4x: Add necessary synchronization for sysreg access

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@...aro.org>
Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....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 128390f9b7fd..366fae810b55 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -187,6 +187,15 @@ 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,
@@ -265,6 +274,10 @@ 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