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

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Message-ID: <CAJ9a7VgTyKfebbYhEG5cGH4HyzU+4FavDXsAxGncXLsDtHSUHA@mail.gmail.com>
Date: Wed, 2 Apr 2025 16:05:10 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>, 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

Hi Leo,


On Tue, 1 Apr 2025 at 19:07, Leo Yan <leo.yan@....com> wrote:
>
> The buffer update callbacks disable the sink before syncing data but
> misses to re-enable it afterward.  This is fine in the general flow,
> because the sink will be re-enabled the next time the PMU event is
> activated.
>
> However, during AUX pause and resume, if the sink is disabled in the
> buffer update callback, there is no chance to re-enable it when AUX
> resumes.
>
> To address this, the callbacks now check the event state
> 'event->hw.state'.  If the event is an active state (0), the sink is
> re-enabled.
>
> For the TMC ETR driver, buffer updates are not fully protected by
> the driver's spinlock.  In this case, the sink is not re-enabled if its
> reference counter is 0, in order to avoid race conditions where the sink
> may have been completely disabled.
>
> Signed-off-by: Leo Yan <leo.yan@....com>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etf.c |  9 +++++++++
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 10 ++++++++++
>  2 files changed, 19 insertions(+)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index d858740001c2..7584cc03d8e6 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -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.

Does the  ETB case need to be handled? - somewhat confusingly the
coresight-tmc-etf.c file handles both ETF and ETB.

Regards

Mike


>  out:
>         raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 76a8cb29b68a..8923fbc6e1a0 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -1636,6 +1636,7 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
>         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>         struct etr_perf_buffer *etr_perf = config;
>         struct etr_buf *etr_buf = etr_perf->etr_buf;
> +       struct perf_event *event = handle->event;
>
>         raw_spin_lock_irqsave(&drvdata->spinlock, flags);
>
> @@ -1705,6 +1706,15 @@ tmc_update_etr_buffer(struct coresight_device *csdev,
>          */
>         smp_wmb();
>
> +       /*
> +        * 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.
> +        */
> +       raw_spin_lock_irqsave(&drvdata->spinlock, flags);
> +       if (csdev->refcnt && !event->hw.state)
> +               __tmc_etr_enable_hw(drvdata);
> +       raw_spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
>  out:
>         /*
>          * Don't set the TRUNCATED flag in snapshot mode because 1) the
> --
> 2.34.1
>


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