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

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Message-ID: <20250402141228.GL115840@e132581.arm.com>
Date: Wed, 2 Apr 2025 15:12:28 +0100
From: Leo Yan <leo.yan@....com>
To: Mike Leach <mike.leach@...aro.org>
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

On Wed, Apr 02, 2025 at 02:50:22PM +0100, Mike Leach wrote:

[...]

> > > > @@ -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.

Okay, now I understand here avoids to disable source and links for a
sink error.

> then falls through to coresight_disable_path_from() - which
> the original code avoided and which also disables helpers a second
> time.

Seems to me, the conclusion for "disables helpers a second time" is
incorrect.

I checked the coresight_disable_path_from() function, when the current
'nd' is passed to it, it will iterate from the _next_ node after 'nd'.

   /* Here 'nd' will be skipped and start from the next node */
   list_for_each_entry_continue(nd, &path->path_list, link) {
       ...

       coresight_disable_helpers(csdev, path);
   }

This means the _current_ coresight device (here is sink device) will
not disable its helpers.  Could you confirm for this?

Thanks,
Leo