Re: [PATCH] coresight: tmc: Fix TMC mode read in tmc_read_unprepare_etb()

[Mike Leach]

On Tue, 16 Jun 2020 at 05:55, Sai Prakash Ranjan
<saiprakash.ranjan@xxxxxxxxxxxxxx> wrote:
>
> Reading TMC mode register without proper coresight power
> management can lead to exceptions like the one in the call
> trace below in tmc_read_unprepare_etb() when the trace data
> is read after the sink is disabled. So fix this by having
> a check for coresight sysfs mode before reading TMC mode
> management register in tmc_read_unprepare_etb() similar to
> tmc_read_prepare_etb().
>
>   SError Interrupt on CPU6, code 0xbe000411 -- SError
>   pstate: 80400089 (Nzcv daIf +PAN -UAO)
>   pc : tmc_read_unprepare_etb+0x74/0x108
>   lr : tmc_read_unprepare_etb+0x54/0x108
>   sp : ffffff80d9507c30
>   x29: ffffff80d9507c30 x28: ffffff80b3569a0c
>   x27: 0000000000000000 x26: 00000000000a0001
>   x25: ffffff80cbae9550 x24: 0000000000000010
>   x23: ffffffd07296b0f0 x22: ffffffd0109ee028
>   x21: 0000000000000000 x20: ffffff80d19e70e0
>   x19: ffffff80d19e7080 x18: 0000000000000000
>   x17: 0000000000000000 x16: 0000000000000000
>   x15: 0000000000000000 x14: 0000000000000000
>   x13: 0000000000000000 x12: 0000000000000000
>   x11: 0000000000000000 x10: dfffffd000000001
>   x9 : 0000000000000000 x8 : 0000000000000002
>   x7 : ffffffd071d0fe78 x6 : 0000000000000000
>   x5 : 0000000000000080 x4 : 0000000000000001
>   x3 : ffffffd071d0fe98 x2 : 0000000000000000
>   x1 : 0000000000000004 x0 : 0000000000000001
>   Kernel panic - not syncing: Asynchronous SError Interrupt
>
> Fixes: 4525412a5046 ("coresight: tmc: making prepare/unprepare functions generic")
> Reported-by: Mike Leach <mike.leach@xxxxxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
> ---
>  drivers/hwtracing/coresight/coresight-tmc-etf.c | 13 ++++++-------
>  1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 36cce2bfb744..6375504ba8b0 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -639,15 +639,14 @@ int tmc_read_unprepare_etb(struct tmc_drvdata *drvdata)
>
>         spin_lock_irqsave(&drvdata->spinlock, flags);
>
> -       /* There is no point in reading a TMC in HW FIFO mode */
> -       mode = readl_relaxed(drvdata->base + TMC_MODE);
> -       if (mode != TMC_MODE_CIRCULAR_BUFFER) {
> -               spin_unlock_irqrestore(&drvdata->spinlock, flags);
> -               return -EINVAL;
> -       }
> -
>         /* Re-enable the TMC if need be */
>         if (drvdata->mode == CS_MODE_SYSFS) {
> +               /* There is no point in reading a TMC in HW FIFO mode */
> +               mode = readl_relaxed(drvdata->base + TMC_MODE);
> +               if (mode != TMC_MODE_CIRCULAR_BUFFER) {
> +                       spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +                       return -EINVAL;
> +               }
>                 /*
>                  * The trace run will continue with the same allocated trace
>                  * buffer. As such zero-out the buffer so that we don't end
>
> base-commit: 3d439a6c349778f129de19595db564a8366c3634
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
>

Tested OK on my DB410c / Linux 5.8-rc1

Tested-by: Mike Leach <mike.leach@xxxxxxxxxx>

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK