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

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Message-ID: <20250313144005.GQ9682@e132581.arm.com>
Date: Thu, 13 Mar 2025 14:40:05 +0000
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>
Cc: lcherian@...vell.com, coresight@...ts.linaro.org,
	Mike Leach <mike.leach@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Alexandre Torgue <alexandre.torgue@...s.st.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 4/7] coresight: Add claim tag warnings and debug messages

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@...aro.org>
> ---
>  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.

> +               /* There was a race setting the tag, clean up and fail */
> +               coresight_clear_self_claim_tag(csa);
>                 return -EBUSY;
> 
> -       coresight_set_self_claim_tag(&csdev->access);
> -       if (coresight_is_claimed_self_hosted(&csdev->access))
> -               return 0;
> -       /* There was a race setting the tag, clean up and fail */
> -       coresight_clear_self_claim_tag(&csdev->access);
> -       return -EBUSY;
> +       case CORESIGHT_CLAIM_EXTERNAL:
> +               /* External debug is an expected state, so log and report BUSY */
> +               dev_dbg(&csdev->dev, "Busy: Claimed by external debugger");
> +               return -EBUSY;
> +
> +       default:
> +       case CORESIGHT_CLAIM_SELF_HOSTED:
> +       case CORESIGHT_CLAIM_INVALID:
> +               /*
> +                * Warn here because we clear a lingering self hosted tag
> +                * on probe, so other tag combinations are impossible.
> +                */
> +               dev_err_once(&csdev->dev, "Invalid claim tag state: %x", tag);
> +               return -EBUSY;
> +       }
>  }
>  EXPORT_SYMBOL_GPL(coresight_claim_device_unlocked);
> 
> @@ -205,7 +217,7 @@ EXPORT_SYMBOL_GPL(coresight_claim_device);
>   */
>  void coresight_disclaim_device_unlocked(struct csdev_access *csa)
>  {
> -       if (coresight_is_claimed_self_hosted(csa))
> +       if (coresight_read_claim_tags(csa) == CORESIGHT_CLAIM_SELF_HOSTED)
>                 coresight_clear_self_claim_tag(csa);
>         else
>                 /*
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index cc7ff1e36ef4..a83113225797 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -36,7 +36,10 @@ extern const struct device_type coresight_dev_type[];
>   * See PSCI - ARM DEN 0022D, Section: 6.8.1 Debug and Trace save and restore.
>   */
>  #define CORESIGHT_CLAIM_MASK           GENMASK(1, 0)
> -#define CORESIGHT_CLAIM_SELF_HOSTED    BIT(1)
> +#define CORESIGHT_CLAIM_FREE           0
> +#define CORESIGHT_CLAIM_EXTERNAL       1
> +#define CORESIGHT_CLAIM_SELF_HOSTED    2
> +#define CORESIGHT_CLAIM_INVALID                3
> 
>  #define TIMEOUT_US             100
>  #define BMVAL(val, lsb, msb)   ((val & GENMASK(msb, lsb)) >> lsb)
> --
> 2.34.1
> 
> _______________________________________________
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