Re: [PATCH] coresight: cti: Add PM runtime call in enable_store

[Jinlong Mao]

On 1/5/2023 9:55 PM, James Clark wrote:
> On 04/01/2023 13:11, James Clark wrote:
> > On 24/12/2022 14:17, Mao Jinlong wrote:
> > > In commit 6746eae4bbad ("coresight: cti: Fix hang in cti_disable_hw()")
> > > PM runtime calls are removed from cti_enable_hw/cti_disable_hw. When
> > > enabling CTI by writing enable sysfs node, clock for accessing CTI
> > > register won't be enabled. Device will crash due to register access
> > > issue. Add PM runtime call in enable_store to fix this issue.
> > >
> > > Signed-off-by: Mao Jinlong <quic_jinlmao@xxxxxxxxxxx>
> > > ---
> > >   drivers/hwtracing/coresight/coresight-cti-sysfs.c | 11 +++++++++--
> > >   1 file changed, 9 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/hwtracing/coresight/coresight-cti-sysfs.c b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > > index 6d59c815ecf5..b1ed424ae043 100644
> > > --- a/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > > +++ b/drivers/hwtracing/coresight/coresight-cti-sysfs.c
> > > @@ -108,10 +108,17 @@ static ssize_t enable_store(struct device *dev,
> > >   	if (ret)
> > >   		return ret;
> > >   
> > > -	if (val)
> > > +	if (val) {
> > > +		ret = pm_runtime_resume_and_get(dev->parent);
> > > +		if (ret)
> > > +			return ret;
> > >   		ret = cti_enable(drvdata->csdev);
> > > -	else
> > > +		if (ret)
> > > +			pm_runtime_put(dev->parent);
> > > +	} else {
> > >   		ret = cti_disable(drvdata->csdev);
> > > +		pm_runtime_put(dev->parent);
> > Hi Jinlong,
> >
> > This new pm_runtime_put() causes this when writing 0 to enable:
> >
> >    [  483.253814] coresight-cti 23020000.cti: Runtime PM usage count
> > underflow!
> >
> > Maybe we can modify cti_disable_hw() to return a value to indicate that
> > the disable actually happened, and only then call pm_runtime_put().
> >
> > I suppose you could also check in the store function if it was already
> > enabled first, but then I don't know what kind of locking that would
> > need? cti_disable_hw() already seems to have a couple of locks, so maybe
> > the return value solution is easiest.
> We've also just seen another issue where multiple calls to
> cti_disable_hw() can cause enable_req_count to go negative. I'm going to
> work on a few fixes (including yours) to make sure that it's complete
> and post it shortly.
Ok, Thank you, James.
> James