Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs_add/remove - Abhishek Pandit-Subedi

From: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	"open list:BLUETOOTH DRIVERS" <linux-bluetooth@vger.kernel.org>,
	ChromeOS Bluetooth Upstreaming 
	<chromeos-bluetooth-upstreaming@chromium.org>,
	Rafael Wysocki <rafael.j.wysocki@intel.com>,
	Stephen Boyd <swboyd@chromium.org>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>
Subject: Re: [PATCH v4 1/1] power: Emit changed uevent on wakeup_sysfs_add/remove
Date: Tue, 7 Jul 2020 10:18:15 -0700	[thread overview]
Message-ID: <CANFp7mXEB4ckWKRDDqUdmBBrbk00CW_pOX+1zmo_AgywtHZ+Nw@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0iVXbxHzV0Y_y5idkoS4DdF+cXQ6kmA0bWWHWZ-TVv8wg@mail.gmail.com>

Sounds good to me. Patch v5 incoming after compile-test.

Thanks
Abhishek

On Tue, Jul 7, 2020 at 10:16 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Tue, Jul 7, 2020 at 6:48 PM Abhishek Pandit-Subedi
> <abhishekpandit@chromium.org> wrote:
> >
> > Hi Rafael,
> >
> > (resent in plain text)
> >
> > On Tue, Jul 7, 2020 at 9:28 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> > >
> > > On Tue, Jul 7, 2020 at 6:24 PM Abhishek Pandit-Subedi
> > > <abhishekpandit@chromium.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@chromium.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");
>
> Yes, which is confusing, because the wakeup attributes may in fact
> have been added.  Which is my point.
>
> >
> > So I'm ok with either keeping this as-is (caller isn't getting
> > confused, just logging) or swallowing the return of kobject_uevent.
>
> I would just ignore the return value of kobject_uevent() along the
> lines of wakeup_sysfs_remove() below.
>
> Thanks!
>
> > > >  }
> > > >
> > > >  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
> > > >