Re: [PATCH v6 08/13] coresight: etm4x: remove redundant call etm4_enable_hw() with hotplug

[Yeoreum Yun <yeoreum.yun@arm.com>]

Hi Leo,

> On Wed, Apr 22, 2026 at 02:21:58PM +0100, Yeoreum Yun wrote:
> 
> [...]
> 
> > +	/*
> > +	 * Take the hotplug lock to prevent redundant calls to etm4_enable_hw().
> > +	 *
> > +	 * The cpu_online_mask is set at the CPUHP_BRINGUP_CPU step.
> > +	 * In other words, if etm4_enable_sysfs() is called between
> > +	 * CPUHP_BRINGUP_CPU and CPUHP_AP_ARM_CORESIGHT_STARTING,
> > +	 * etm4_enable_hw() may be invoked in etm4_enable_sysfs_smp_call()
> > +	 * and then executed again in etm4_starting_cpu().
> > +	 */
> > +	cpus_read_lock();
> >  	ret = smp_call_function_single(drvdata->cpu,
> >  				       etm4_enable_sysfs_smp_call, &arg, 1);
> > +	cpus_read_unlock();
> 
> This will cause double deadlock with the patch:
> https://lore.kernel.org/linux-arm-kernel/20260511-arm_coresight_path_power_management_improvement-v12-6-1c9dcb1de8c9@arm.com/#t
> 
> I think we need to drop this one.

As I asked on another thread, Are we're going to merge your patch first?
If not, we need to sustain it anyway.

Thanks.

-- 
Sincerely,
Yeoreum Yun