Thank you, this was indeed the issue.

For anyone who is interested, i have disabled the power down on idle with these commands:

$ echo 1 > /sys/devices/system/cpu/cpu1/cpuidle/state1/disable $ echo 1 > /sys/devices/system/cpu/cpu1/cpuidle/state0/disable

This disables the power down on IDLE on CPU1.

Thanks, Mike.

On Mon, Apr 9, 2018 at 5:39 PM, Mathieu Poirier mathieu.poirier@linaro.org wrote:

On 9 April 2018 at 08:12, Mike Leach Mike.Leach@arm.com wrote:

...

Hi,

Ensure that you have disabled core power down on idle when using sysfs

to manipulate etm devices.

...

The ETM devices are on the same power/clock as the CPUs, so if the CPU

powers down on idle then the ETM will be powered down too.

...

Writing to a device that is unpowered will usually kill your system.

Mike is correct - you are facing a core power down problems. When vendors don't honour TRCPDCR.PU (as it is the case with the dragon board) cpuIDLE must be disabled or core must be prevented from reaching deep idle state.

Mathieu

...

Regards

Mike

-----Original Message----- From: CoreSight coresight-bounces@lists.linaro.org On Behalf Of Mike

Bazov

...

Sent: 09 April 2018 14:24 To: coresight@lists.linaro.org Subject: Using coresight via sysfs freezes my entire system.

Greetings,

I'm enabling a sink(ETR) via sysfs:

$ echo "1"> /sys/bus/coresight/devices/826000.etr/enable_sink

And the sink is enabled successfully.

Now, i try to turn on a random ETMv4 source, so i just choose this one:

$ echo "1" > /sys/bus/coresight/devices/85c000.etm/enable_source

And this freezes my entire system. This ETMv4 is for CPU 0.. So i tried

to turn on(after a reboot, and enabling a sink again) the next ETMv4(for CPU 1):

...

$ echo "1" > /sys/bus/coresight/devices/85d000.etm/enable_source

And i can see the kernel logs are happy, and tracing is(assuming the

logs are true) enabled:

...

[ 61.495119] coresight-tmc 826000.etr: TMC-ETR enabled [ 61.495150] coresight-dynamic-replicator 824000.replicator:

REPLICATOR enabled

...

[ 61.499261] coresight-tmc 825000.etf: TMC-ETF enabled [ 61.506468] coresight-funnel 821000.funnel: FUNNEL inport 4 enabled [ 61.511438] coresight-funnel 841000.funnel: FUNNEL inport 1 enabled [ 61.517635] coresight-etm4x 85d000.etm: ETM tracing enabled

But when i try to turn it off:

$ echo "0" > /sys/bus/coresight/devices/85d000.etm/enable_source

This freezes my entire system.. again.

I'm using the perf-opencsd-master kernel(https://github.com/

Linaro/perf-opencsd https://github.com/Linaro/perf-opencsd ), and the Dragonboard 410c.

...

Any ideas, hints?

Thank you.

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...

---

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