[PATCH v4 2/2] coresight: core: Disable helpers for devices that fail to enable

[Yabin Cui]

On Wed, Apr 23, 2025 at 2:32 AM Leo Yan <leo.yan at arm.com> wrote:
>
> On Tue, Apr 15, 2025 at 11:46:49AM -0700, Yabin Cui wrote:
> > When enabling a SINK or LINK type coresight device fails, the
> > associated helpers should be disabled.
> >
> > Signed-off-by: Yabin Cui <yabinc at google.com>
> > Suggested-by: Suzuki K Poulose <suzuki.poulose at arm.com>
> > ---
> >  drivers/hwtracing/coresight/coresight-core.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > index fb43ef6a3b1f..d9fcea69d221 100644
> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -486,8 +486,10 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
> >                        * that need disabling. Disabling the path here
> >                        * would mean we could disrupt an existing session.
> >                        */
> > -                     if (ret)
> > +                     if (ret) {
> > +                             coresight_disable_helpers(csdev, path);
>
> I think we can do better for code consolidation - we can use a central
> place for error handling.  I will give details below.
>
> >                               goto out;
> > +                     }
> >                       break;
> >               case CORESIGHT_DEV_TYPE_SOURCE:
> >                       /* sources are enabled from either sysFS or Perf */
> > @@ -497,15 +499,17 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
> >                       child = list_next_entry(nd, link)->csdev;
> >                       ret = coresight_enable_link(csdev, parent, child, source);
> >                       if (ret)
> > -                             goto err;
> > +                             goto err_disable_helpers;
> >                       break;
> >               default:
> > -                     goto err;
> > +                     goto err_disable_helpers;
>
> I know this is not a problem introduced by your patch - for an error
> case, it returns 0.  This will hide unexpected issues.  I would like
> to suggest to return -EINVAL for unknown types.
>
> >               }
> >       }
> >
> >  out:
> >       return ret;
> > +err_disable_helpers:
> > +     coresight_disable_helpers(csdev, path);
> >  err:
> >       coresight_disable_path_from(path, nd);
> >       goto out;
>
> I am just wandering if we can handle errors in a unified way and
> without using goto.  I would change the code as below.
>
> The point is to use a general flow for error handling, include a
> sink error.  For sink error, we still invoke
> coresight_disable_path_from() for an empty operation.
>
> Also, I think we need an additional patch for error handling in
> coresight_enable_helpers(). If any errors are detected while enabling
> a helper, we should disable the helpers that have already been
> enabled.
>
> Please let me know if you have any questions.

I'm fine with these changes. However, there's one spot below that's
controversial in the v2 patch.

>
> Thanks,
> Leo
>
> ---8<---
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index fb43ef6a3b1f..cf2a3708a05e 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_disable_path;
>                 /*
>                  * ETF devices are tricky... They can be a link or a sink,
>                  * depending on how they are configured.  If an ETF has been
> @@ -487,7 +487,7 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
>                          * would mean we could disrupt an existing session.
>                          */
>                         if (ret)
> -                               goto out;
> +                               goto err_disable_helpers;

I made a similar change in this area in the v2 patch, which
contradicts the original comment here.
Mike had concerns about it. I explained my reasoning, but haven't
heard back. Could we get confirmation
that it's safe to remove the comment and proceed to err_disable_helpers here?

>                         break;
>                 case CORESIGHT_DEV_TYPE_SOURCE:
>                         /* sources are enabled from either sysFS or Perf */
> @@ -497,18 +497,21 @@ int coresight_enable_path(struct coresight_path *path, enum cs_mode mode,
>                         child = list_next_entry(nd, link)->csdev;
>                         ret = coresight_enable_link(csdev, parent, child, source);
>                         if (ret)
> -                               goto err;
> +                               goto err_disable_helpers;
>                         break;
>                 default:
> -                       goto err;
> +                       ret = -EINVAL;
> +                       goto err_disable_helpers;
>                 }
>         }
>
> -out:
> -       return ret;
> -err:
> +       return 0;
> +
> +err_disable_helpers:
> +       coresight_disable_helpers(csdev, path);
> +err_disable_path:
>         coresight_disable_path_from(path, nd);
> -       goto out;
> +       return ret;
>  }
>
> > --
> > 2.49.0.604.gff1f9ca942-goog
> >