linux-kernel - Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs

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Date:   Tue, 7 Jul 2020 09:47:52 -0700
From:   Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        "open list:BLUETOOTH DRIVERS" <linux-bluetooth@...r.kernel.org>,
        ChromeOS Bluetooth Upstreaming 
        <chromeos-bluetooth-upstreaming@...omium.org>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Stephen Boyd <swboyd@...omium.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs_add/remove

Hi Rafael,

(resent in plain text)

On Tue, Jul 7, 2020 at 9:28 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Tue, Jul 7, 2020 at 6:24 PM Abhishek Pandit-Subedi
> <abhishekpandit@...omium.org> wrote:
> >
> > Udev rules that depend on the power/wakeup attribute don't get triggered
> > correctly if device_set_wakeup_capable is called after the device is
> > created. This can happen for several reasons (driver sets wakeup after
> > device is created, wakeup is changed on parent device, etc) and it seems
> > reasonable to emit a changed event when adding or removing attributes on
> > the device.
> >
> > Signed-off-by: Abhishek Pandit-Subedi <abhishekpandit@...omium.org>
> > ---
> >
> > Changes in v4:
> > - Fix warning where returning from void and tested on device
> >
> > Changes in v3:
> > - Simplified error handling
> >
> > Changes in v2:
> > - Add newline at end of bt_dev_err
> >
> >  drivers/base/power/sysfs.c | 9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/base/power/sysfs.c b/drivers/base/power/sysfs.c
> > index 24d25cf8ab1487..aeb58d40aac8de 100644
> > --- a/drivers/base/power/sysfs.c
> > +++ b/drivers/base/power/sysfs.c
> > @@ -1,6 +1,7 @@
> >  // SPDX-License-Identifier: GPL-2.0
> >  /* sysfs entries for device PM */
> >  #include <linux/device.h>
> > +#include <linux/kobject.h>
> >  #include <linux/string.h>
> >  #include <linux/export.h>
> >  #include <linux/pm_qos.h>
> > @@ -739,12 +740,18 @@ int dpm_sysfs_change_owner(struct device *dev, kuid_t kuid, kgid_t kgid)
> >
> >  int wakeup_sysfs_add(struct device *dev)
> >  {
> > -       return sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
> > +       int ret = sysfs_merge_group(&dev->kobj, &pm_wakeup_attr_group);
> > +
> > +       if (ret)
> > +               return ret;
> > +
> > +       return kobject_uevent(&dev->kobj, KOBJ_CHANGE);
>
> So let me repeat the previous comment:
>
> If you return an error here, it may confuse the caller to think that
> the operation has failed completely, whereas the merging of the
> attribute group has been successful already.
>
> I don't think that an error can be returned at this point.
>

The caller looks at the return code and just logs that an error
occurred (no other action). It's also unlikely for kobject_uevent to
fail (I saw mostly -ENOMEM and an -ENOENT when the kobj wasn't in the
correct set).

Call site:
    int ret = wakeup_sysfs_add(dev);

    if (ret)
        dev_info(dev, "Wakeup sysfs attributes not added\n");

So I'm ok with either keeping this as-is (caller isn't getting
confused, just logging) or swallowing the return of kobject_uevent.

> >  }
> >
> >  void wakeup_sysfs_remove(struct device *dev)
> >  {
> >         sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
> > +       kobject_uevent(&dev->kobj, KOBJ_CHANGE);
> >  }
> >
> >  int pm_qos_sysfs_add_resume_latency(struct device *dev)
> > --
> > 2.27.0.212.ge8ba1cc988-goog
> >