Re: [PATCH] coresight: etm4x: fix mis-usage of nr_resource in sysfs interface

Mathieu Poirier
2020-09-08T17:37:32Z

On Fri, Sep 04, 2020 at 06:08:46PM +0800, Zhouwen (Jonathan, Turing) wrote:
>
> Hi Mathieu,
>
> Thanks for your review.
>
> 在 2020/9/4 1:22, Mathieu Poirier 写道:
> > On Wed, Sep 02, 2020 at 03:52:56PM +0800, Jonathan Zhou wrote:
> > > The member @nr_resource represents how many resource selector pairs,
> > > and the pair 0 is always implemented and reserved.
> > > So let's multiply by 2 when displaying the implemented resource seletors
> > > and resetting the seletor configuration .
> > > And also update the validation of the input @idx.
> > >
> > > Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> > > Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> > > Cc: Mike Leach <mike.leach@linaro.org>
> > > Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
> > > Cc: lizixian@hisilicon.com
> > > Signed-off-by: Jonathan Zhou <jonathan.zhouwen@huawei.com>
> > > ---
> > > drivers/hwtracing/coresight/coresight-etm4x-sysfs.c | 15 ++++++++++-----
> > > 1 file changed, 10 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > index b673e738bc9a..635b93d20efa 100644
> > > --- a/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > +++ b/drivers/hwtracing/coresight/coresight-etm4x-sysfs.c
> > > @@ -143,8 +143,10 @@ static ssize_t nr_resource_show(struct device *dev,
> > > {
> > > unsigned long val;
> > > struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > > -
> > > - val = drvdata->nr_resource;
> > > + /* @nr_resource represents how many resource selector pairs,
> > > + * hence multiply by 2.
> >
> > Your comment said it correctly, @nr_resource present the number of _pairs_. As
> > such the code is correct and there is no need to multiply by 2.
> >
>
> Sorry for not mentioned the reason of modified this. From the function
> @res_ctrl_store, we can see that only one individual resource selector can
> be accessed via the ->res_idx. Therefore, it may be better to show the
> number of individual resource selectors.

The end result does not change, i.e this entry represent the number of pairs
available on the system.

>
> > > + */
> > > + val = 2 * drvdata->nr_resource;
> > > return scnprintf(buf, PAGE_SIZE, "%#lx\n", val);
> > > }
> > > static DEVICE_ATTR_RO(nr_resource);
> > > @@ -236,7 +238,7 @@ static ssize_t reset_store(struct device *dev,
> > > }
> > > config->res_idx = 0x0;
> > > - for (i = 0; i < drvdata->nr_resource; i++)
> > > + for (i = 2; i < 2 * drvdata->nr_resource; i++)
> > > config->res_ctrl[i] = 0x0;
> >
> > This hunk is correct - please send a patch for it.
>
> Ok.
>
> >
> > > config->ss_idx = 0x0;
> > > @@ -1663,8 +1665,11 @@ static ssize_t res_idx_store(struct device *dev,
> > > if (kstrtoul(buf, 16, &val))
> > > return -EINVAL;
> > > - /* Resource selector pair 0 is always implemented and reserved */
> > > - if ((val == 0) || (val >= drvdata->nr_resource))
> > > + /*
> > > + * Resource selector pair 0 is always implemented and reserved,
> > > + * namely an idx with 0 and 1 is illegal.
> > > + */
> > > + if ((val == 0) || (val == 1) || (val >= 2 * drvdata->nr_resource))
> > > return -EINVAL;
> >
> > The index, i.e ->res_idx, represent pairs an not individual resource.
> >
> > Thanks,
> > Mathieu
> >
>
> If we want all of the ->res_ctrl accessable, the ->res_idx should represent
> individual resource. That's the reason.

I see your point now. I think the above condition should be simplified:

if ((val < 2) || (val >= 2 * drvdata->nr_resource))

>
> Best regards.
>
> Jonathan.
>
> > > /*
> > > --
> > > 1.9.1
> > >
> > .
> >