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

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Message-ID: <20250206103213.GB8855@e132581.arm.com>
Date: Thu, 6 Feb 2025 10:32:13 +0000
From: Leo Yan <leo.yan@....com>
To: Yuanfang Zhang <quic_yuanfang@...cinc.com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@...aro.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	kernel@...cinc.com, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight-tmc: stop disabling tmc when flush timeout

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?

> 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

> Signed-off-by: Yuanfang Zhang <quic_yuanfang@...cinc.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@...cinc.com>
> 
>