linux-kernel - Re: [PATCH v2 1/3] coresight: catu: Introduce refcount and spinlock for enabling/disabling

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Message-ID: <CALJ9ZPMx7vqjgkn8OApLBAPwF35v=enHc07A==LXG0C+922rag@mail.gmail.com>
Date: Thu, 3 Apr 2025 10:53:12 -0700
From: Yabin Cui <yabinc@...gle.com>
To: Leo Yan <leo.yan@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach <mike.leach@...aro.org>, 
	James Clark <james.clark@...aro.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] coresight: catu: Introduce refcount and spinlock
 for enabling/disabling

On Wed, Apr 2, 2025 at 6:01 AM Leo Yan <leo.yan@....com> wrote:
>
> Hi Yabin,
>
> On Tue, Apr 01, 2025 at 06:21:59PM -0700, Yabin Cui wrote:
>
> [...]
>
> > > @@ -486,12 +491,17 @@ static int catu_disable_hw(struct catu_drvdata *drvdata)
> > >
> > >  static int catu_disable(struct coresight_device *csdev, void *__unused)
> > >  {
> > > -       int rc;
> > > +       int rc = 0;
> > >         struct catu_drvdata *catu_drvdata = csdev_to_catu_drvdata(csdev);
> > > +       guard(raw_spinlock_irqsave)(&catu_drvdata->spinlock);
> > >
> > > -       CS_UNLOCK(catu_drvdata->base);
> > > -       rc = catu_disable_hw(catu_drvdata);
> > > -       CS_LOCK(catu_drvdata->base);
> > > +       if (--csdev->refcnt == 0) {
> > > +               CS_UNLOCK(catu_drvdata->base);
> > > +               rc = catu_disable_hw(catu_drvdata);
> > > +               CS_LOCK(catu_drvdata->base);
> > > +       } else {
> > > +               rc = -EBUSY;
>
> This is not an error if the decremented reference counter is not zero.
> It should return 0.  Otherwise, the change looks good to me.

In coresight_disable_helpers(), the return value of catu_disable()
isn't checked.
The -EBUSY return was used for consistency with other refcounted
disable functions
like tmc_disable_etf_sink() and tmc_disable_etr_sink(). I'm happy to
change it back
to 0 if you believe that would be the more accurate return value here.

>
> Thanks,
> Leo