linux-kernel - Re: [PATCH v4 5/7] coresight: tmc: Re-enable sink after buffer update

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Message-ID: <CAJ9a7VjDe9U9RufKfuBAW9gAUdiWHyErxqsV=3gL=oaj7uS12Q@mail.gmail.com>
Date: Thu, 24 Apr 2025 18:27:27 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: James Clark <james.clark@...aro.org>, Jonathan Corbet <corbet@....net>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] coresight: tmc: Re-enable sink after buffer update

On Wed, 2 Apr 2025 at 16:58, Leo Yan <leo.yan@....com> wrote:
>
> Hi Mike,
>
> On Wed, Apr 02, 2025 at 04:05:10PM +0100, Mike Leach wrote:
>
> [...]
>
> > > @@ -482,6 +482,7 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
> > >         unsigned long offset, to_read = 0, flags;
> > >         struct cs_buffers *buf = sink_config;
> > >         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> > > +       struct perf_event *event = handle->event;
> > >
> > >         if (!buf)
> > >                 return 0;
> > > @@ -586,6 +587,14 @@ static unsigned long tmc_update_etf_buffer(struct coresight_device *csdev,
> > >          * is expected by the perf ring buffer.
> > >          */
> > >         CS_LOCK(drvdata->base);
> > > +
> > > +       /*
> > > +        * If the event is active, it is triggered during an AUX pause.
> > > +        * Re-enable the sink so that it is ready when AUX resume is invoked.
> > > +        */
> > > +       if (!event->hw.state)
> > > +               __tmc_etb_enable_hw(drvdata);
> > > +
> >
> > Think that the  refcnt should be checked here too.
>
> No, ETF driver uses spinlock to guard the entire region for checking
> refcnt and updating buffer, here it is still in the same critical
> region.  This is why the checking refcnt is not needed.
>
> > Does the  ETB case need to be handled? - somewhat confusingly the
> > coresight-tmc-etf.c file handles both ETF and ETB.
>
> ETF is for the link mode, and ETB is for sink.  Updating buffer is only
> for sink mode, this is why here I use __tmc_etb_enable_hw().  Does it
> make sense?
>
> I also have a question for the paired operations (this is applied for
> both ETF and ETR drivers).
>
> Now the flow is:
>
>   tmc_update_etf_buffer()  {
>
>     tmc_flush_and_stop();
>
>     update buffer;
>
>     __tmc_etb_enable_hw();
>   }
>
> The operations are not paired between tmc_flush_and_stop() and
> __tmc_etb_enable_hw().
>
> The tmc_flush_and_stop() function only controls the TMC_FFCR register.
> I'm not sure whether I need to extract the TMC_FFCR operations from
> __tmc_etb_enable_hw() to use them for recovery in the update buffer.
> Or do you think re-enabling the hardware in this patch is the safer
> approach?
>
> Thanks,
> Leo

Looks OK to me.

Reviewed-by: Mike Leach <mike.leach@...aro.org>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK