Re: [PATCH] coresight: tmc: Read TMC mode only when TMC hw is enabled

[Sai Prakash Ranjan]

Hi Mathieu,

On 2020-04-13 22:44, Mathieu Poirier wrote:
> On Mon, Apr 13, 2020 at 01:55:30PM +0530, Sai Prakash Ranjan wrote:
> > Hi Suzuki,
> >
> > On 2020-04-13 04:47, Suzuki K Poulose wrote:
> > > Hi Sai,
> > >
> > > On 04/09/2020 12:35 PM, Sai Prakash Ranjan wrote:
> > > > Reading TMC mode register in tmc_read_prepare_etb without
> > > > enabling the TMC hardware leads to async exceptions like
> > > > the one in the call trace below. This can happen if the
> > > > user tries to read the TMC etf data via device node without
> > > > setting up source and the sink first which enables the TMC
> > > > hardware in the path. So make sure that the TMC is enabled
> > > > before we try to read TMC data.
> > >
> > > So, one can trigger the same SError by simply :
> > >
> > > $ cat /sys/bus/coresight/device/tmc_etb0/mgmt/mode
> > >
> >
> > I do not see any SError when I run the above command.
> >
> > localhost ~ # cat /sys/bus/coresight/devices/tmc_etf0/mgmt/mode
> > 0x0
> >
> > And this is most likely due to
> >
> > commit cd9e3474bb793dc ("coresight: add PM runtime calls to
> > coresight_simple_func()")
>
> Ok, so this is related to power management (you can ignore my question 
> in the
> previous email).
>
> Regarding function tmc_read_prepare_etb(), the best way to deal with 
> this is
> probably make sure drvdata->mode != CS_MODE_DISABLED before reading 
> TMC_MODE.
> If there is a buffer to read it will have been copied when the ETB was 
> disabled
> and there won't be a need to access the HW.

This works as well, thanks.

diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c 
b/drivers/hwtracing/coresight/coresight-tmc-etf.c
index d0cc3985b72a..7ffe05930984 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
@@ -596,6 +596,11 @@ int tmc_read_prepare_etb(struct tmc_drvdata 
*drvdata)
                goto out;
        }

+       if (drvdata->mode == CS_MODE_DISABLED) {
+               ret = -EINVAL;
+               goto out;
+       }
+
        /* 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) {


Thanks,
Sai

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