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

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Date:   Wed, 14 Sep 2022 23:00:39 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Bhupesh Sharma <bhupesh.sharma@...aro.org>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        mathieu.poirier@...aro.org, mike.leach@...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 v2] coresight: etm4x: Fix crash observed on Qcom ETM
 parts with 'Low power override'

On Wed, Sep 14, 2022 at 03:43:53PM +0100, Suzuki Kuruppassery Poulose wrote:

[...]

> > > +	/*
> > > +	 * 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().

Agreed, this is more clear.

[...]

> > 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),      \
>         })

Thanks a lot for explaination, sorry for noise.

Leo