linux-kernel - Re: [PATCH] coresight: tmc: fix for trace collection bug in sysFS mode

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Message-ID: <CANLsYkzNqMuwcmYJtoORXrON54Wt1oj5uyp2NQpKYM2AN4F26g@mail.gmail.com>
Date:   Tue, 13 Sep 2016 09:41:52 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Venkatesh Vivekanandan <venkatesh.vivekanandan@...adcom.com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] coresight: tmc: fix for trace collection bug in sysFS mode

On 13 September 2016 at 06:20, Venkatesh Vivekanandan
<venkatesh.vivekanandan@...adcom.com> wrote:
> tmc_etb_dump_hw is never called in sysFS mode to collect trace from
> hardware, because drvdata->mode is set to CS_MODE_DISABLED at
> tmc_disable_etf/etr_sink
>
> static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
> {
>         .
>         .
>         if (local_read(&drvdata->mode) == CS_MODE_SYSFS)
>                 tmc_etb_dump_hw(drvdata);
>         .
>         .
> }
>
> static void tmc_disable_etf_sink(struct coresight_device *csdev)
> {
>        .
>        .
>         val = local_xchg(&drvdata->mode, CS_MODE_DISABLED);
>         /* Disable the TMC only if it needs to */
>         if (val != CS_MODE_DISABLED)
>                 tmc_etb_disable_hw(drvdata);

You are correct.

>        .
>        .
> }
>
> Signed-off-by: Venkatesh Vivekanandan <venkatesh.vivekanandan@...adcom.com>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etf.c | 9 +++++----
>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 9 +++++----
>  2 files changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 466af86..c7fb7f7 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -61,6 +61,8 @@ static void tmc_etb_dump_hw(struct tmc_drvdata *drvdata)
>
>  static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>  {
> +       long val;
> +
>         CS_UNLOCK(drvdata->base);
>
>         tmc_flush_and_stop(drvdata);
> @@ -68,7 +70,8 @@ static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>          * When operating in sysFS mode the content of the buffer needs to be
>          * read before the TMC is disabled.
>          */
> -       if (local_read(&drvdata->mode) == CS_MODE_SYSFS)
> +       val = local_xchg(&drvdata->mode, CS_MODE_DISABLED);
> +       if (val == CS_MODE_SYSFS)
>                 tmc_etb_dump_hw(drvdata);
>         tmc_disable_hw(drvdata);
>
> @@ -225,7 +228,6 @@ static int tmc_enable_etf_sink(struct coresight_device *csdev, u32 mode)
>
>  static void tmc_disable_etf_sink(struct coresight_device *csdev)
>  {
> -       long val;
>         unsigned long flags;
>         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> @@ -235,9 +237,8 @@ static void tmc_disable_etf_sink(struct coresight_device *csdev)
>                 return;
>         }
>
> -       val = local_xchg(&drvdata->mode, CS_MODE_DISABLED);
>         /* Disable the TMC only if it needs to */
> -       if (val != CS_MODE_DISABLED)
> +       if (local_read(&drvdata->mode) != CS_MODE_DISABLED)
>                 tmc_etb_disable_hw(drvdata);

This would work but tmc_enable_etf_sink() and tmc_disable_etf_sink()
are no longer balanced.  Another approach would be to add a "mode"
parameter to tmc_etb_disable_hw() and so something like:

if (val != CS_MODE_DISABLED)
        tmc_etb_disable_hw(drvdata, val);

In tmc_etb_disable_hw(), if mode == CS_MODE_SYSFS then we can move
ahead with the dump operation.  The same apply for ETR.

Thanks,
Mathieu

>
>         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 688be9e..480794b 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -73,6 +73,8 @@ static void tmc_etr_dump_hw(struct tmc_drvdata *drvdata)
>
>  static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>  {
> +       long val;
> +
>         CS_UNLOCK(drvdata->base);
>
>         tmc_flush_and_stop(drvdata);
> @@ -80,7 +82,8 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>          * When operating in sysFS mode the content of the buffer needs to be
>          * read before the TMC is disabled.
>          */
> -       if (local_read(&drvdata->mode) == CS_MODE_SYSFS)
> +       val = local_xchg(&drvdata->mode, CS_MODE_DISABLED);
> +       if (val == CS_MODE_SYSFS)
>                 tmc_etr_dump_hw(drvdata);
>         tmc_disable_hw(drvdata);
>
> @@ -215,7 +218,6 @@ static int tmc_enable_etr_sink(struct coresight_device *csdev, u32 mode)
>
>  static void tmc_disable_etr_sink(struct coresight_device *csdev)
>  {
> -       long val;
>         unsigned long flags;
>         struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> @@ -225,9 +227,8 @@ static void tmc_disable_etr_sink(struct coresight_device *csdev)
>                 return;
>         }
>
> -       val = local_xchg(&drvdata->mode, CS_MODE_DISABLED);
>         /* Disable the TMC only if it needs to */
> -       if (val != CS_MODE_DISABLED)
> +       if (local_read(&drvdata->mode) != CS_MODE_DISABLED)
>                 tmc_etr_disable_hw(drvdata);
>
>         spin_unlock_irqrestore(&drvdata->spinlock, flags);
> --
> 2.1.0
>