Hi Yabin

On 17/08/2023 22:06, Yabin Cui wrote:

Hi coresight driver maintainers,

I am from the Android toolchain team. I am trying to use ETE (Embedded Trace Extension). But on my device, the system crashes when the ETM driver is trying to read TRCDEVARCH via sysreg interface.

When you say crashes, what exactly is reported ? Does the kernel get an exception ? Or system hangs completely ?

I suspect :

1) You are running some hyp at EL2, which doesn't allow accessing the TRC* registers and injects a Illegal instruction ? 2) If not the above, the ETE is not powered (very unlikely)

Suzuki

In https://github.com/torvalds/linux/blob/master/drivers/hwtracing/coresight/co... https://github.com/torvalds/linux/blob/master/drivers/hwtracing/coresight/coresight-etm4x-core.c#L1045 :

static bool etm4_init_sysreg_access(struct etmv4_drvdata *drvdata,    struct csdev_access *csa) { u32 devarch;

if (!cpu_supports_sysreg_trace())   <- this returns true return false;

/*

• ETMs implementing sysreg access must implement TRCDEVARCH.

*/ devarch = read_etm4x_sysreg_const_offset(TRCDEVARCH);  <- never see the message logged immediately after this line, so should abort here.   ... }

Do you have any suggestions on how I can debug the problem? Is there any other place making sysreg interface to ETE not accessible? Or can the ETE sysreg interface not be implemented? I tried the memory mapped register interface of ETE, it works fine. The only change I need is to bypass the devarch version check in etm4_init_iomem_access, in in https://github.com/torvalds/linux/blob/master/drivers/hwtracing/coresight/co... https://github.com/torvalds/linux/blob/master/drivers/hwtracing/coresight/coresight-etm4x-core.c#L1082 I wonder if we can allow iomem access for ETE if the sysreg access doesn't work on some devices.

Thanks, Yabin