Re: [PATCH] coresight-tmc: stop disabling tmc when flush timeout

[Yuanfang Zhang <quic_yuanfang@quicinc.com>]

On 2/6/2025 6:32 PM, Leo Yan wrote:
> Hi Yuanfang,
> 
> On Fri, Jan 03, 2025 at 04:01:54PM +0800, Yuanfang Zhang wrote:
>>
>> When multiple ETMs are enabled simultaneously, the time required
>> to complete a flush in the process of reading the TMC device node
>> may exceed the default wait time of 100us.
> 
> Have you tried how long time would be safe to wait for the
> TMCREADY_BIT bit to be set on your platform?
yes, 400000us.
> 
>> If the TMC capture is stopped while any ETM has not completed its
>> flush, it can cause the corresponding CPU to hang.
>>
>> Fix the by checking the TMCReady bit after the flush. If TMCReady
>> bit is set, TraceCaptEn bit can be clear; otherwise, return directly
>> and stop the TMC read.
> 
> When a timeout for TMC flush and stop is detected, if the driver
> arbitrarily bails out without disabling TMC, this would leave the
> hardware always on.
> 
> I would like first know if a longer timeout can fix the issue.
> 
> Thanks,
> Leo
> 
yes, longer timeout can fix this issue.

>> Signed-off-by: Yuanfang Zhang <quic_yuanfang@quicinc.com>
>> ---
>>  drivers/hwtracing/coresight/coresight-tmc-etf.c | 17 +++++++++++++++--
>>  drivers/hwtracing/coresight/coresight-tmc-etr.c | 22 +++++++++++++++++-----
>>  2 files changed, 32 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> index d4f641cd9de69488fe3d1c1dc9b5a9eafb55ed59..bded290c42891d782344d9a6e63ebdbed6719133 100644
>> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
>> @@ -80,11 +80,21 @@ static void tmc_etb_dump_hw(struct tmc_drvdata *drvdata)
>>         return;
>>  }
>>
>> -static void __tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>> +static int __tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>>  {
>> +       int rc;
>> +
>>         CS_UNLOCK(drvdata->base);
>>
>>         tmc_flush_and_stop(drvdata);
>> +
>> +       rc = tmc_wait_for_tmcready(drvdata);
>> +       if (rc) {
>> +               dev_err(&drvdata->csdev->dev,
>> +                       "Failed to disable : TMC is not ready\n");
>> +               CS_LOCK(drvdata->base);
>> +               return rc;
>> +       }
>>         /*
>>          * When operating in sysFS mode the content of the buffer needs to be
>>          * read before the TMC is disabled.
>> @@ -94,6 +104,7 @@ static void __tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>>         tmc_disable_hw(drvdata);
>>
>>         CS_LOCK(drvdata->base);
>> +       return 0;
>>  }
>>
>>  static void tmc_etb_disable_hw(struct tmc_drvdata *drvdata)
>> @@ -650,7 +661,9 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
>>                         ret = -EINVAL;
>>                         goto out;
>>                 }
>> -               __tmc_etb_disable_hw(drvdata);
>> +               ret = __tmc_etb_disable_hw(drvdata);
>> +               if (ret)
>> +                       goto out;
>>         }
>>
>>         drvdata->reading = true;
>> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> index a48bb85d0e7f44a25b813f3c828cc3d705d16012..63a1f7501562fa0b5c2fe6ea53dce4d82842bec3 100644
>> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
>> @@ -1135,11 +1135,21 @@ static void tmc_etr_sync_sysfs_buf(struct tmc_drvdata *drvdata)
>>         }
>>  }
>>
>> -static void __tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>> +static int __tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>>  {
>> +       int rc;
>> +
>>         CS_UNLOCK(drvdata->base);
>>
>>         tmc_flush_and_stop(drvdata);
>> +
>> +       rc = tmc_wait_for_tmcready(drvdata);
>> +       if (rc) {
>> +               dev_err(&drvdata->csdev->dev,
>> +                       "Failed to disable : TMC is not ready\n");
>> +               CS_LOCK(drvdata->base);
>> +               return rc;
>> +       }
>>         /*
>>          * When operating in sysFS mode the content of the buffer needs to be
>>          * read before the TMC is disabled.
>> @@ -1150,7 +1160,7 @@ static void __tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>>         tmc_disable_hw(drvdata);
>>
>>         CS_LOCK(drvdata->base);
>> -
>> +       return 0;
>>  }
>>
>>  void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>> @@ -1779,9 +1789,11 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
>>         }
>>
>>         /* Disable the TMC if we are trying to read from a running session. */
>> -       if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
>> -               __tmc_etr_disable_hw(drvdata);
>> -
>> +       if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS) {
>> +               ret = __tmc_etr_disable_hw(drvdata);
>> +               if (ret)
>> +                       goto out;
>> +       }
>>         drvdata->reading = true;
>>  out:
>>         spin_unlock_irqrestore(&drvdata->spinlock, flags);
>>
>> ---
>> base-commit: fac04efc5c793dccbd07e2d59af9f90b7fc0dca4
>> change-id: 20250103-fix_cpu_hung-b5a95179ada4
>>
>> Best regards,
>> --
>> Yuanfang Zhang <quic_yuanfang@quicinc.com>
>>
>>