[PATCH] coresight: Fix disabling of CoreSight TPIU

[robert.walker@arm.com (Robert Walker)]

Hi Mathieu,

> -----Original Message-----
> From: Mathieu Poirier [mailto:mathieu.poirier at linaro.org]
> Sent: 27 November 2017 17:30
> To: Robert Walker <Robert.Walker@arm.com>
> Cc: linux-arm-kernel at lists.infradead.org; CoreSight at lists.linaro.org
> Subject: Re: [PATCH] coresight: Fix disabling of CoreSight TPIU
> 
> Hi Robert,
> 
> On 24 November 2017 at 02:58, Robert Walker <robert.walker@arm.com>
> wrote:
> > The CoreSight TPIU should be disabled when tracing to other sinks to
> > allow them to operate at full bandwidth.
> >
> > This patch fixes tpiu_disable_hw() to correctly disable the TPIU by
> > configuring the TPIU to stop on flush, initiating a manual flush,
> > waiting for the flush to complete and then waits for the TPIU to
> > indicate it has stopped.
> >
> > Signed-off-by: Robert Walker <robert.walker@arm.com>
> > ---
> >  drivers/hwtracing/coresight/coresight-tpiu.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-tpiu.c
> > b/drivers/hwtracing/coresight/coresight-tpiu.c
> > index bef49a3..4b46c49 100644
> > --- a/drivers/hwtracing/coresight/coresight-tpiu.c
> > +++ b/drivers/hwtracing/coresight/coresight-tpiu.c
> > @@ -46,8 +46,11 @@
> >  #define TPIU_ITATBCTR0         0xef8
> >
> >  /** register definition **/
> > +/* FFSR - 0x300 */
> > +#define FFSR_FT_STOPPED                BIT(1)
> >  /* FFCR - 0x304 */
> >  #define FFCR_FON_MAN           BIT(6)
> > +#define FFCR_STOP_FI           BIT(12)
> >
> >  /**
> >   * @base:      memory mapped base address for this component.
> > @@ -85,10 +88,14 @@ static void tpiu_disable_hw(struct tpiu_drvdata
> > *drvdata)  {
> >         CS_UNLOCK(drvdata->base);
> >
> > -       /* Clear formatter controle reg. */
> > -       writel_relaxed(0x0, drvdata->base + TPIU_FFCR);
> > +       /* Clear formatter and stop on flush */
> > +       writel_relaxed(FFCR_STOP_FI, drvdata->base + TPIU_FFCR);
> >         /* Generate manual flush */
> > -       writel_relaxed(FFCR_FON_MAN, drvdata->base + TPIU_FFCR);
> > +       writel_relaxed(FFCR_STOP_FI | FFCR_FON_MAN, drvdata->base +
> TPIU_FFCR);
> > +       /* Wait for flush to complete */
> > +       coresight_timeout(drvdata->base, TPIU_FFCR, FFCR_FON_MAN, 0);
> > +       /* Wait for formatter to stop */
> > +       coresight_timeout(drvdata->base, TPIU_FFSR, FFSR_FT_STOPPED,
> > + 1);
> >
> >         CS_LOCK(drvdata->base);
> >  }
> 
> Shouldn't we also do this at boot time when the TPIU in _probed() ?
> That way the TPIU doesn't have to explicitly be enabled and disabled prior to
> running other tracing sessions.
> 
> Thanks,
> Mathieu

There already is a call to tpiu_disable_hw() in tpiu_probe(), so the TPIU is disabled on boot.
When tracing to another sink (e.g. ETR), the TPIU won't be enabled / disabled (i.e. tpiu_enable_hw() and tpiu_disable_hw() won't be called) as it's not on the direct path from source to sink.

Regards

Rob

> 
> 
> > --
> > 1.9.1
> >