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

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Message-ID: <CAH=2NtyBCfuz+dtO47mNNjcojQg0H776KjD9XJyxVhOTpGm1Qw@mail.gmail.com>
Date:   Thu, 4 Aug 2022 20:49:33 +0530
From:   Bhupesh Sharma <bhupesh.sharma@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        mathieu.poirier@...aro.org, mike.leach@...aro.org,
        leo.yan@...aro.org, alexander.shishkin@...ux.intel.com,
        linux-kernel@...r.kernel.org, bhupesh.linux@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] coresight: etm4x: Fix crash observed on Qcom ETM parts
 with 'Low power override'

Hi Suzuki,

On Thu, 4 Aug 2022 at 19:02, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>
> 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@...aro.org>
> > Cc: Suzuki K Poulose <suzuki.poulose@....com>
> > Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Signed-off-by: Bhupesh Sharma <bhupesh.sharma@...aro.org>
> > ---
> >   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.

Sure, let me fix this in v2.

Regards,
Bhupesh

> >       major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);
>