Re: [PATCH v2] coresight: etm4x: Handle accesses to TRCSTALLCTLR

[Suzuki K Poulose <suzuki.poulose@xxxxxxx>]

On 1/27/21 5:43 PM, Mathieu Poirier wrote:
> Good day,
>
> On Wed, Jan 27, 2021 at 12:00:32PM +0000, Suzuki K Poulose wrote:
> > TRCSTALLCTLR register is only implemented if
> >
> >     TRCIDR3.STALLCTL == 0b1
> >
> > Make sure the driver touches the register only it is implemented.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
> > Cc: Leo Yan <leo.yan@xxxxxxxxxx>
> > Cc: Mike Leach <mike.leach@xxxxxxxxxx>
> > Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> > ---
> > Changes since v1:
> >    - No change to the patch, fixed the stable email address and
> >      added usual reviewers.
> > ---
> >   drivers/hwtracing/coresight/coresight-etm4x-core.c  | 9 ++++++---
> >   drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 3 +++
> >   2 files changed, 9 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index b40e3c2bf818..814b49dae0c7 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -367,7 +367,8 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
> >   	etm4x_relaxed_write32(csa, 0x0, TRCAUXCTLR);
> >   	etm4x_relaxed_write32(csa, config->eventctrl0, TRCEVENTCTL0R);
> >   	etm4x_relaxed_write32(csa, config->eventctrl1, TRCEVENTCTL1R);
> > -	etm4x_relaxed_write32(csa, config->stall_ctrl, TRCSTALLCTLR);
> > +	if (drvdata->stallctl)
> > +		etm4x_relaxed_write32(csa, config->stall_ctrl, TRCSTALLCTLR);
> >   	etm4x_relaxed_write32(csa, config->ts_ctrl, TRCTSCTLR);
> >   	etm4x_relaxed_write32(csa, config->syncfreq, TRCSYNCPR);
> >   	etm4x_relaxed_write32(csa, config->ccctlr, TRCCCCTLR);
> > @@ -1545,7 +1546,8 @@ static int etm4_cpu_save(struct etmv4_drvdata *drvdata)
> >   	state->trcauxctlr = etm4x_read32(csa, TRCAUXCTLR);
> >   	state->trceventctl0r = etm4x_read32(csa, TRCEVENTCTL0R);
> >   	state->trceventctl1r = etm4x_read32(csa, TRCEVENTCTL1R);
> > -	state->trcstallctlr = etm4x_read32(csa, TRCSTALLCTLR);
> > +	if (drvdata->stallctl)
> > +		state->trcstallctlr = etm4x_read32(csa, TRCSTALLCTLR);
> >   	state->trctsctlr = etm4x_read32(csa, TRCTSCTLR);
> >   	state->trcsyncpr = etm4x_read32(csa, TRCSYNCPR);
> >   	state->trcccctlr = etm4x_read32(csa, TRCCCCTLR);
> > @@ -1657,7 +1659,8 @@ static void etm4_cpu_restore(struct etmv4_drvdata *drvdata)
> >   	etm4x_relaxed_write32(csa, state->trcauxctlr, TRCAUXCTLR);
> >   	etm4x_relaxed_write32(csa, state->trceventctl0r, TRCEVENTCTL0R);
> >   	etm4x_relaxed_write32(csa, state->trceventctl1r, TRCEVENTCTL1R);
> > -	etm4x_relaxed_write32(csa, state->trcstallctlr, TRCSTALLCTLR);
> > +	if (drvdata->stallctl)
> > +		etm4x_relaxed_write32(csa, state->trcstallctlr, TRCSTALLCTLR);
> >   	etm4x_relaxed_write32(csa, state->trctsctlr, TRCTSCTLR);
> >   	etm4x_relaxed_write32(csa, state->trcsyncpr, TRCSYNCPR);
> >   	etm4x_relaxed_write32(csa, state->trcccctlr, TRCCCCTLR);
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > index 1c490bcef3ad..cd9249fbf913 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > @@ -296,6 +296,9 @@ static ssize_t mode_store(struct device *dev,
> >   	if (kstrtoul(buf, 16, &val))
> >   		return -EINVAL;
> >   
> > +	if ((val & ETM_MODE_ISTALL_EN) && !drvdata->stallctl)
> > +		return -EINVAL;
> > +
>
> We have two choices here:
>
> 1) Follow what is already done in this function for implementation define
> options like ETM_MODE_BB, ETMv4_MODE_CTXID, ETM_MODE_RETURNSTACK and others.  In
> that case we would have:
>
>          /* bit[8], Instruction stall bit */
>          if ((config->mode & ETM_MODE_ISTALL_EN) && drvdata->stallctl == true))
>                  config->stall_ctrl |= BIT(8);
>          else
>                  config->stall_ctrl &= ~BIT(8);
>
> 2) Return -EINVAL when something is not supported, like you have above.  In that
> case we'd have to enact the same behavior for all the options, which has the > potential of breaking user space.

I did think about this and but now I agree  1 is better for now. I will respin.


Cheers
Suzuki