Hi Bhupesh,

On Thu, Aug 25, 2022 at 10:52:32AM +0530, 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.

Fixes: 5214b563588e ("coresight: etm4x: Add support for sysreg only devices") Cc: Mike Leach mike.leach@linaro.org Cc: Suzuki K Poulose suzuki.poulose@arm.com Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Bhupesh Sharma bhupesh.sharma@linaro.org

---

• v1 can be seen here: https://lore.kernel.org/lkml/20220803191236.3037591-1-bhupesh.sharma@linaro....
• 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;
  

I personally think this sentence should be placed in the function etm4_probe(), you need to move it just before smp call etm4_init_arch_data(), this can allow DT property "qcom,skip-power-up" to be respected.

/* * 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;

I prefer to move the condition checking for "desc.access.io_mem" to etm4_init_sysreg_access(), this can make sure the flag skip_power_up is set correctly based on property of system register access.

A side topic, in the mainline kernel I found the value "desc.access.io_mem" is always zero (see the initialized value in etm4_probe() and etm4_init_sysreg_access()). Should we initialize desc.access.io_mem to true in etm4_probe()?

diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index d39660a3e50c..cf2555c50abb 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -1939,6 +1939,7 @@ static int etm4_probe(struct device *dev, void __iomem *base, u32 etm_pid) if (drvdata->cpu < 0) return drvdata->cpu;

+ desc.access.io_mem = true; init_arg.drvdata = drvdata; init_arg.csa = &desc.access; init_arg.pid = etm_pid;

Thanks, Leo

major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);

2.35.3