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

[Yuanfang Zhang <quic_yuanfang@quicinc.com>]

On 1/3/2025 4:01 PM, 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. 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.
> 
> 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,

gently reminder.