linux-kernel - Re: [PATCH v2 03/28] coresight: etm3x: Always set tracer's device mode on target CPU

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Message-ID: <20250702104246.GW794930@e132581.arm.com>
Date: Wed, 2 Jul 2025 11:42:46 +0100
From: Leo Yan <leo.yan@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Yabin Cui <yabinc@...gle.com>, Keita Morisaki <keyz@...gle.com>,
	Yuanfang Zhang <quic_yuanfang@...cinc.com>,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 03/28] coresight: etm3x: Always set tracer's device
 mode on target CPU

On Wed, Jul 02, 2025 at 11:18:21AM +0100, Yeoreum Yun wrote:
> Hi Leo,
> 
> [...]
> > @@ -464,17 +477,29 @@ static int etm_enable_perf(struct coresight_device *csdev,
> >  			   struct perf_event *event,
> >  			   struct coresight_path *path)
> >  {
> > +	int ret = 0;
> >  	struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> >
> > -	if (WARN_ON_ONCE(drvdata->cpu != smp_processor_id()))
> > -		return -EINVAL;
> > +	if (!coresight_take_mode(csdev, CS_MODE_PERF))
> > +		return -EBUSY;
> > +
> > +	if (WARN_ON_ONCE(drvdata->cpu != smp_processor_id())) {
> > +		ret = -EINVAL;
> > +		goto out;
> > +	}
> 
> Small question: why drvdata->cpu != smp_processor_id() check after
> changing mode? Would it better to check before change of it?

You are right. I will update in next version.

Thanks for pointing out this!

Leo