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

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Message-ID: <a4bce4f5-88c3-4755-9ac5-3ce6fb78dfbf@linaro.org>
Date: Mon, 17 Mar 2025 11:56:17 +0000
From: James Clark <james.clark@...aro.org>
To: Leo Yan <leo.yan@....com>
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 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@...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.
> 

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