linux-kernel - [PATCH v2] coresight: etm4x: Fix crash observed on Qcom ETM parts with 'Low power override'

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Date:   Thu, 25 Aug 2022 10:52:32 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org
Cc:     mathieu.poirier@...aro.org, suzuki.poulose@....com,
        mike.leach@...aro.org, leo.yan@...aro.org,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org,
        bhupesh.linux@...il.com,
        Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH v2] coresight: etm4x: Fix crash observed on Qcom ETM parts with 'Low power override'

Some Qualcomm ETM implementations require skipping powering up
the trace unit, as the ETMs are in the same power domain as
their CPU cores.

Via commit 5214b563588e ("coresight: etm4x: Add support for
sysreg only devices"), the setting of 'skip_power_up' flag was
moved after the 'etm4_init_arch_data' function is called, whereas
the flag value is itself used inside the function. This causes
a crash when ETM mode 'Low-power state behavior override' is set
on some Qualcomm parts.

Fix the same.

Fixes: 5214b563588e ("coresight: etm4x: Add support for sysreg only devices")
Cc: Mike Leach <mike.leach@...aro.org>
Cc: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@...aro.org>
---
 - v1 can be seen here: https://lore.kernel.org/lkml/20220803191236.3037591-1-bhupesh.sharma@linaro.org/
 - Addressed the review comments from Suzuki.
 - Rebased on linux-next.

 drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index d39660a3e50c..14c1c7869795 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -977,6 +977,16 @@ static bool etm4_init_sysreg_access(struct etmv4_drvdata *drvdata,
 	if (!cpu_supports_sysreg_trace())
 		return false;
 
+	/*
+	 * Some Qualcomm implementations require skipping powering up the trace unit,
+	 * as the ETMs are in the same power domain as their CPU cores.
+	 *
+	 * Since the 'skip_power_up' flag is used inside 'etm4_init_arch_data' function,
+	 * initialize it before the function is called.
+	 */
+	if (fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
+		drvdata->skip_power_up = true;
+
 	/*
 	 * ETMs implementing sysreg access must implement TRCDEVARCH.
 	 */
@@ -1951,8 +1961,7 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
 		return -EINVAL;
 
 	/* TRCPDCR is not accessible with system instructions. */
-	if (!desc.access.io_mem ||
-	    fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
+	if (!desc.access.io_mem)
 		drvdata->skip_power_up = true;
 
 	major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);
-- 
2.35.3