Re: [PATCH 4/9] coresight-tpdm: Add reset node to TPDM node

[Tao Zhang]

Hi Suzuki,

在 10/24/2022 6:10 PM, Suzuki K Poulose 写道:
> On 08/09/2022 09:45, Tao Zhang wrote:
> > TPDM device need a node to reset the configurations and status of
> > it. This change provides a node to reset the configurations and
> > disable the TPDM if it has been enabled.
>
> It is not clear to me *why* this is needed. Please could you
> elaborate on the use case of this ? See my questions below.
For example, we usually reset the configuration through the "reset"
node before using a TPDM, so as to avoid the previous configuration
affecting the current use. And in some scenarios, it may be necessary
to reset the TPDM configuration to complete the verification of certain
function.
> > Signed-off-by: Tao Zhang <quic_taozha@xxxxxxxxxxx>
> > ---
> >   drivers/hwtracing/coresight/coresight-tpdm.c | 32 
> > ++++++++++++++++++++++++++++
> >   1 file changed, 32 insertions(+)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-tpdm.c 
> > b/drivers/hwtracing/coresight/coresight-tpdm.c
> > index 69ea453..74cc653 100644
> > --- a/drivers/hwtracing/coresight/coresight-tpdm.c
> > +++ b/drivers/hwtracing/coresight/coresight-tpdm.c
> > @@ -152,6 +152,37 @@ static void tpdm_init_default_data(struct 
> > tpdm_drvdata *drvdata)
> >       }
> >   }
> >   +static ssize_t reset_store(struct device *dev,
> > +                      struct device_attribute *attr,
> > +                      const char *buf,
> > +                      size_t size)
>
> minor nit: Alignment
I will update this in the next patch series.
> > +{
> > +    int ret = 0;
> > +    unsigned long val;
> > +    struct tpdm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > +
> > +    ret = kstrtoul(buf, 10, &val);
>
> So, any integer value written to the sysfs knob triggers the rest ?
> It may be better to restrict this to "1".
Make sense, I will update this in the next patch series.
> > +    if (ret)
> > +        return ret;
> > +
> > +    spin_lock(&drvdata->spinlock);
> > +    /* Reset all datasets to ZERO */
> > +    if (drvdata->dsb != NULL)
> > +        memset(drvdata->dsb, 0, sizeof(struct dsb_dataset));
> > +
> > +    /* Init the default data */
> > +    tpdm_init_default_data(drvdata);
>
> Why is this needed ? Does the DSB device configuration change
> on the fly ?
We usually reset the configuration through the "reset" node at the
beginning of using a TPDM. DSB related elements need to be initialized
before configuring them.
The TPDM is usually to be used by the following sequence.
Reset(initialization) -> Configure -> Enable to use
> > +
> > +    spin_unlock(&drvdata->spinlock);
> > +
> > +    /* Disable tpdm if enabled */
> > +    if (drvdata->enable)
> > +        coresight_disable(drvdata->csdev);
>
> Why is this needed ? Isn't this supposed to be triggered from the "path"
> when the trace session is complete ?
In some scenarios, it may be necessary to reset the TPDM configuration
in the process of verification and re-configure the TPDM. If this is the
case, we need to disable the TPDM first, and re-configure before enabling
it again.
> Suzuki
>
> > +
> > +    return size;
> > +}
> > +static DEVICE_ATTR_WO(reset);
> > +
> >   /*
> >    * value 1: 64 bits test data
> >    * value 2: 32 bits test data
> > @@ -192,6 +223,7 @@ static ssize_t integration_test_store(struct 
> > device *dev,
> >   static DEVICE_ATTR_WO(integration_test);
> >     static struct attribute *tpdm_attrs[] = {
> > +    &dev_attr_reset.attr,
> >       &dev_attr_integration_test.attr,
> >       NULL,
> >   };
Best Regards
Tao