linux-kernel - Re: [PATCH] power:sysfs: Expose device wakeup_event

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Date:   Tue, 23 Jul 2019 09:43:55 -0700
From:   Ravi Chandra Sadineni <ravisadineni@...omium.org>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        x86@...nel.org, rjw@...ysocki.net, pavel@....cz,
        len.brown@...el.com, bhe@...hat.com, dyoung@...hat.com,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-pm@...r.kernel.org, Todd Broch <tbroch@...omium.org>
Subject: Re: [PATCH] power:sysfs: Expose device wakeup_event_count.

Hi Greg,

On Mon, Jul 22, 2019 at 11:22 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>
> On Mon, Jul 22, 2019 at 11:02:58AM -0700, Ravi Chandra Sadineni wrote:
> > Device level event_count can help user level daemon to track if a
> > praticular device has seen an wake interrupt during a suspend resume
> > cycle. Thus expose it via sysfs.
> >
> > Signed-off-by: Ravi Chandra Sadineni <ravisadineni@...omium.org>
> > ---
> >  Documentation/ABI/testing/sysfs-devices-power | 11 ++++++++++
> >  drivers/base/power/sysfs.c                    | 20 +++++++++++++++++++
> >  2 files changed, 31 insertions(+)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-devices-power b/Documentation/ABI/testing/sysfs-devices-power
> > index 1ca04b4f0489..344549f4013f 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-power
> > +++ b/Documentation/ABI/testing/sysfs-devices-power
> > @@ -89,6 +89,17 @@ Description:
> >               attribute is not present. If the device is not enabled to wake
> >               up the system from sleep states, this attribute is empty.
> >
> > +What:                /sys/devices/.../power/wakeup_event_count
> > +Date:                July 2019
> > +Contact:     Ravi Chandra sadineni <ravisadineni@...omium.org>
> > +Description:
> > +             The /sys/devices/.../wakeup_event_count attribute contains the
> > +             number of signaled wakeup events associated with the device.
> > +             This attribute is read-only. If the device is not capable to
> > +             wake up the system from sleep states, this attribute is not
> > +             present. If the device is not enabled to wake up the system
> > +             from sleep states, this attribute is empty.
>
> The attribute is not "empty" it returns just an empty line.
Corrected the description.
>
> Is that really a good thing if you are expecting a number?
This is to adhere to the convention as described in
base/power/sysfs.c. Hope this is o.k
>
> > +
> >  What:                /sys/devices/.../power/wakeup_active_count
> >  Date:                September 2010
> >  Contact:     Rafael J. Wysocki <rjw@...ysocki.net>
> > diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> > index f42044d9711c..8dc1235b9784 100644
> > --- a/drivers/base/power/sysfs.c
> > +++ b/drivers/base/power/sysfs.c
> > @@ -357,6 +357,25 @@ static ssize_t wakeup_count_show(struct device *dev,
> >
> >  static DEVICE_ATTR_RO(wakeup_count);
> >
> > +static ssize_t wakeup_event_count_show(struct device *dev,
> > +                              struct device_attribute *attr, char *buf)
> > +{
> > +     unsigned long count = 0;
> > +     bool enabled = false;
> > +
> > +     spin_lock_irq(&dev->power.lock);
> > +     if (dev->power.wakeup) {
> > +             count = dev->power.wakeup->event_count;
> > +             enabled = true;
> > +     }
> > +     spin_unlock_irq(&dev->power.lock);
>
> Why do you need to lock?  The state and count can change right after the
> lock, so what does this help with?
power.wakeup can be NULL (device_wakeup_detach ()) if wakeup is
disabled for a particular device.
>
> > +     return enabled ? sprintf(buf, "%lu\n", count) : sprintf(buf, "\n");
>
> Use a real if statement please.
>
> > +}
> > +
> > +static DEVICE_ATTR_RO(wakeup_event_count);
> > +
> > +
> > +
>
> too many empty lines :)
Removed the empty lines.
>
> thanks,
>
> greg k-h

Thanks,
Ravi