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

[Suzuki K Poulose]

On 13/09/2022 11:52, Leo Yan wrote:
> 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@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>
> > ---
> >   - v1 can be seen here: https://lore.kernel.org/lkml/20220803191236.3037591-1-bhupesh.sharma@xxxxxxxxxx/
> >   - 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.

Or we could move this to init_iomem_access() and explicitly set the flag
to true in init_sysreg_access().

> >   	/*
> >   	 * 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.

+1

> 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()?

Thats not true. It is initialised at :

etm4_init_iomem_access():

	*csa = CSDEV_ACCESS_IOMEM(drvdata->base);

Where

#define CSDEV_ACCESS_IOMEM(_addr)               \
        ((struct csdev_access)  {               \
                .io_mem         = true,         \
                .base           = (_addr),      \
        })



Suzuki