Re: [PATCH] coresight: etm4x: Fix crash observed on Qcom ETM parts with 'Low power override'

From: Suzuki K Poulose
Date: Thu Aug 04 2022 - 09:32:40 EST


Hi Bhupesh,


On 03/08/2022 20:12, Bhupesh Sharma wrote:
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.


Thanks for the patch. The patch is correct. But please see my comment
below.

Fixes: 5214b563588e ("coresight: etm4x: Add support for sysreg only devices")
Cc: Mike Leach <mike.leach@xxxxxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@xxxxxxxxxx>
---
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..cf6254b87fd5 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -1943,6 +1943,16 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid)
init_arg.csa = &desc.access;
init_arg.pid = etm_pid;
+ /*
+ * 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;
+
if (smp_call_function_single(drvdata->cpu,
etm4_init_arch_data, &init_arg, 1))
dev_err(dev, "ETM arch init failed\n");
@@ -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;

Please could you move this setting into "etm4_init_sysreg_access()" ? It looks a bit odd to split the check in the same function. Moving this to
the sysreg_access() makes it explicit.

Suzuki



major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);