Re: [PATCH 4/7] coresight: Add claim tag warnings and debug messages

[James Clark]

On 13/03/2025 2:40 pm, Leo Yan wrote:
> On Tue, Feb 11, 2025 at 10:39:40AM +0000, James Clark wrote:
> > Add a dev_dbg() message so that external debugger conflicts are more
> > visible. There are multiple reasons for -EBUSY so a message for this
> > particular one could be helpful. Add errors for and enumerate all the
> > other cases that are impossible.
> >
> > Signed-off-by: James Clark <james.clark@xxxxxxxxxx>
> > ---
> >   drivers/hwtracing/coresight/coresight-core.c | 48 ++++++++++++--------
> >   drivers/hwtracing/coresight/coresight-priv.h |  5 +-
> >   2 files changed, 34 insertions(+), 19 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> > index 7b53165c93af..7fe5d5d432c4 100644
> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -133,16 +133,6 @@ static inline u32 coresight_read_claim_tags(struct csdev_access *csa)
> >                           csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMCLR));
> >   }
> >
> > -static inline bool coresight_is_claimed_self_hosted(struct csdev_access *csa)
> > -{
> > -       return coresight_read_claim_tags(csa) == CORESIGHT_CLAIM_SELF_HOSTED;
> > -}
> > -
> > -static inline bool coresight_is_claimed_any(struct coresight_device *csdev)
> > -{
> > -       return coresight_read_claim_tags(&csdev->access) != 0;
> > -}
> > -
> >   static inline void coresight_set_self_claim_tag(struct csdev_access *csa)
> >   {
> >          csdev_access_relaxed_write32(csa, CORESIGHT_CLAIM_SELF_HOSTED,
> > @@ -169,18 +159,40 @@ static inline void coresight_clear_self_claim_tag(struct csdev_access *csa)
> >    */
> >   int coresight_claim_device_unlocked(struct coresight_device *csdev)
> >   {
> > +       int tag;
> > +       struct csdev_access *csa;
> > +
> >          if (WARN_ON(!csdev))
> >                  return -EINVAL;
> >
> > -       if (coresight_is_claimed_any(csdev))
> > +       csa = &csdev->access;
> > +       tag = coresight_read_claim_tags(csa);
> > +
> > +       switch (tag) {
> > +       case CORESIGHT_CLAIM_FREE:
> > +               coresight_set_self_claim_tag(csa);
> > +               if (coresight_read_claim_tags(csa) == CORESIGHT_CLAIM_SELF_HOSTED)
> > +                       return 0;
> > +
>
> It would be a rare case if a failure happens here.  Seems to me, it
> would be valuable to print a log for this edge case.
>
> Otherwise, looks good to me.

Yeah I can add dev_dbg("Busy: Couldn't set self claim tag"). Just to 
distinguish this race case from the other busy case.