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Message-ID: <CANLsYkyFJx9gSfkMNmxT=bdas=sKFpZ0Cad42gm6nHoyq8FfnA@mail.gmail.com>
Date: Wed, 16 Jan 2019 10:30:16 -0700
From: Mathieu Poirier <mathieu.poirier@...aro.org>
To: Greg KH <gregkh@...uxfoundation.org>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
schwidefsky@...ibm.com, heiko.carstens@...ibm.com,
Will Deacon <will.deacon@....com>,
Mark Rutland <mark.rutland@....com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
Adrian Hunter <adrian.hunter@...el.com>, ast@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
"Suzuki K. Poulose" <suzuki.poulose@....com>,
linux-s390@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/7] coresight: perf: Add "sinks" group to PMU directory
On Wed, 16 Jan 2019 at 10:13, Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Wed, Jan 16, 2019 at 09:38:09AM -0700, Mathieu Poirier wrote:
> > On Wed, 16 Jan 2019 at 09:33, Greg KH <gregkh@...uxfoundation.org> wrote:
> > >
> > > On Wed, Jan 16, 2019 at 09:14:33AM -0700, Mathieu Poirier wrote:
> > > > On Wed, 16 Jan 2019 at 08:39, Greg KH <gregkh@...uxfoundation.org> wrote:
> > > > >
> > > > > On Tue, Jan 15, 2019 at 04:07:37PM -0700, Mathieu Poirier wrote:
> > > > > > Add a "sinks" directory entry so that users can see all the sinks
> > > > > > available in the system in a single place. Individual sink are added
> > > > > > as they are registered with the coresight bus.
> > > > > >
> > > > > > Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> > > > > > ---
> > > > > > .../hwtracing/coresight/coresight-etm-perf.c | 43 +++++++++++++++++++
> > > > > > .../hwtracing/coresight/coresight-etm-perf.h | 1 +
> > > > > > drivers/hwtracing/coresight/coresight.c | 17 ++++++++
> > > > > > 3 files changed, 61 insertions(+)
> > > > > >
> > > > > > diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.c b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > > > index f21eb28b6782..292bd409a68c 100644
> > > > > > --- a/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > > > +++ b/drivers/hwtracing/coresight/coresight-etm-perf.c
> > > > > > @@ -14,6 +14,7 @@
> > > > > > #include <linux/perf_event.h>
> > > > > > #include <linux/percpu-defs.h>
> > > > > > #include <linux/slab.h>
> > > > > > +#include <linux/stringhash.h>
> > > > > > #include <linux/types.h>
> > > > > > #include <linux/workqueue.h>
> > > > > >
> > > > > > @@ -43,8 +44,18 @@ static const struct attribute_group etm_pmu_format_group = {
> > > > > > .attrs = etm_config_formats_attr,
> > > > > > };
> > > > > >
> > > > > > +static struct attribute *etm_config_sinks_attr[] = {
> > > > > > + NULL,
> > > > > > +};
> > > > > > +
> > > > > > +static const struct attribute_group etm_pmu_sinks_group = {
> > > > > > + .name = "sinks",
> > > > > > + .attrs = etm_config_sinks_attr,
> > > > > > +};
> > > > > > +
> > > > > > static const struct attribute_group *etm_pmu_attr_groups[] = {
> > > > > > &etm_pmu_format_group,
> > > > > > + &etm_pmu_sinks_group,
> > > > > > NULL,
> > > > > > };
> > > > > >
> > > > > > @@ -479,6 +490,38 @@ int etm_perf_symlink(struct coresight_device *csdev, bool link)
> > > > > > return 0;
> > > > > > }
> > > > > >
> > > > > > +static ssize_t etm_perf_sink_name_show(struct device *dev,
> > > > > > + struct device_attribute *dattr,
> > > > > > + char *buf)
> > > > > > +{
> > > > > > + /* See function coresight_sink_by_id() to know where this is used */
> > > > > > + u32 hash = hashlen_hash(hashlen_string(NULL, dattr->attr.name));
> > > > > > +
> > > > > > + return scnprintf(buf, PAGE_SIZE, "%x\n", hash);
> > > > > > +}
> > > > > > +
> > > > > > +int etm_perf_symlink_sink(struct coresight_device *csdev)
> > > > > > +{
> > > > > > + struct device *pmu_dev = etm_pmu.dev;
> > > > > > + struct device *pdev = csdev->dev.parent;
> > > > > > + struct device_attribute *dev_attr;
> > > > > > +
> > > > > > + if (csdev->type != CORESIGHT_DEV_TYPE_SINK &&
> > > > > > + csdev->type != CORESIGHT_DEV_TYPE_LINKSINK)
> > > > > > + return -EINVAL;
> > > > > > +
> > > > > > + if (!etm_perf_up)
> > > > > > + return -EPROBE_DEFER;
> > > > > > +
> > > > > > + dev_attr = kzalloc(sizeof(*dev_attr), GFP_KERNEL);
> > > > > > + dev_attr->attr.name = kstrdup(dev_name(pdev), GFP_KERNEL);
> > > > > > + dev_attr->attr.mode = 0444;
> > > > > > + dev_attr->show = etm_perf_sink_name_show;
> > > > > > +
> > > > > > + return sysfs_add_file_to_group(&pmu_dev->kobj,
> > > > > > + &dev_attr->attr, "sinks");
> > > > >
> > > > > What is so odd about this call that you needed me to review this?
> > > >
> > > > As far as I can tell nobody is feeding a dynamic struct attribute to
> > > > the function and I wasn't sure if it was because they were told not to
> > > > or simply because it wasn't needed, hence asking for a second opinion.
> > >
> > > Ah. Well, again, this is a good question to answer:
> > >
> > > > > And what happens if this call fails, do you leak memory?
> >
> > That's something I will fix in the next revision.
> >
> > >
> > > And also, what happens when you unload the device, who frees the
> > > attribute's memory?
> >
> > If configured, coresight devices aren't removable.
>
> But is the driver able to be unloaded? Unbound from the device manually
> through sysfs? There's lots of ways devices are "removed" that don't
> involved physical removal :)
All drivers are built-in and thus preventing them from being unloaded.
They also have their ".suppress_bin_attrs" field set to take care of
unbinding through sysfs.
>
> thanks,
>
> greg k-h
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