linux-kernel - Re: [PATCH v2 3/3] coresight: core: Disable helpers for devices that fail to enable

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Message-ID: <CAJ9a7Vg4DGzPhnSBh2taTgUTORMY3GUPpJY2bHjkMdFB1=wP=Q@mail.gmail.com>
Date: Wed, 2 Apr 2025 14:50:22 +0100
From: Mike Leach <mike.leach@...aro.org>
To: Leo Yan <leo.yan@....com>
Cc: Yabin Cui <yabinc@...gle.com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	James Clark <james.clark@...aro.org>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, coresight@...ts.linaro.org, 
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] coresight: core: Disable helpers for devices that
 fail to enable

Hi,

On Wed, 2 Apr 2025 at 14:32, Leo Yan <leo.yan@....com> wrote:
>
> On Tue, Apr 01, 2025 at 06:22:46PM -0700, Yabin Cui wrote:
> > On Tue, Apr 1, 2025 at 6:19 PM Yabin Cui <yabinc@...gle.com> wrote:
> > >
> > > When enabling a SINK or LINK type coresight device fails, the
> > > associated helpers should be disabled.
> > >
> > > Signed-off-by: Yabin Cui <yabinc@...gle.com>
> > > Suggested-by: Suzuki K Poulose <suzuki.poulose@....com>
> > > ---
> > >  drivers/hwtracing/coresight/coresight-core.c | 12 ++++--------
> > >  1 file changed, 4 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > > index fb43ef6a3b1f..e3270d9b46c9 100644
> > > --- a/drivers/hwtracing/coresight/coresight-core.c
> > > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > > @@ -465,7 +465,7 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
> > >                 /* Enable all helpers adjacent to the path first */
> > >                 ret = coresight_enable_helpers(csdev, mode, path);
> > >                 if (ret)
> > > -                       goto err;
> > > +                       goto err_helper;
> > >                 /*
> > >                  * ETF devices are tricky... They can be a link or a sink,
> > >                  * depending on how they are configured.  If an ETF has been
> > > @@ -480,14 +480,8 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
> > >                 switch (type) {
> > >                 case CORESIGHT_DEV_TYPE_SINK:
> > >                         ret = coresight_enable_sink(csdev, mode, sink_data);
> > > -                       /*
> > > -                        * Sink is the first component turned on. If we
> > > -                        * failed to enable the sink, there are no components
> > > -                        * that need disabling. Disabling the path here
> > > -                        * would mean we could disrupt an existing session.
> > > -                        */
> > >                         if (ret)
> > > -                               goto out;
> > > +                               goto err;

Going to err here is wrong. The comment above specifically states that
we do _not_ want to disable the path, yet the new code flow disables
helpers. then falls through to coresight_disable_path_from() - which
the original code avoided and which also disables helpers a second
time.

Please rework to get the correct program flow.

> > >                         break;
> > >                 case CORESIGHT_DEV_TYPE_SOURCE:
> > >                         /* sources are enabled from either sysFS or Perf */
> > > @@ -507,6 +501,8 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
> > >  out:
> > >         return ret;
> > >  err:
> > > +       coresight_disable_helpers(csdev);

Drop this - put it where it is needed  in the flow

Regards

Mike


>
> Given it is unconditionally to enable helpers, I would suggest we
> disable helper unconditionally.  Thus, we don't need to add a new
> 'err_helper' tag, simply reuse the 'err' tag would be fine.
>
> I would like to know if mainatiners have different opinions.
>
> Thanks,
> Leo
>
> > > +err_helper:
> > >         coresight_disable_path_from(path, nd);
> > >         goto out;
> > >  }
> > > --
> > > 2.49.0.472.ge94155a9ec-goog
> > >

coresight_disable_path_from() also disables helpers.

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK