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

[Suzuki K Poulose]

On 13/09/16 16:41, Mathieu Poirier wrote:
> On 13 September 2016 at 06:20, Venkatesh Vivekanandan
> <venkatesh.vivekanandan@xxxxxxxxxxxx> 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@xxxxxxxxxxxx>
> > ---
> >  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

I think we should :

1) First switch the drvdata->mode to a normal type from local_t. Using an
atomic type for mode is completely unnecessary and comes with the overhead
of barriers/synchronisation instructions, while all accesses, including read/write
are performed under the drvdata->spinlock. I have a patch already for this, which
I plan to send it soon.

and

2) Do something like :

void  tmc_disable_etX_sink()
{
	if (drvdata->mode != CS_MODE_DISABLED) {
		tmc_etX_disable_hw(drvdata);
		drvdata->mode = CS_MODE_DISABLED;
	}
}

Leaving the tmc_etX_disable_hw() untouched.


Suzuki