linux-kernel - Re: [PATCH v3 1/1] power: Emit changed uevent on wakeup_sysfs

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Date:   Tue, 7 Jul 2020 17:53:59 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Abhishek Pandit-Subedi <abhishekpandit@...omium.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@...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 v3 1/1] power: Emit changed uevent on wakeup_sysfs_add/remove

On Tue, Jul 7, 2020 at 5:49 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 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..04c82373c8f240 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);

Returning an error code here may be misleading, because the basic
operation (i.e. merging the attribute group) has succeeded already.

What about printing a message if kobject_uevent() returns an error and
returning 0 anyway?

>  }
>
>  void wakeup_sysfs_remove(struct device *dev)
>  {
>         sysfs_unmerge_group(&dev->kobj, &pm_wakeup_attr_group);
> +       return kobject_uevent(&dev->kobj, KOBJ_CHANGE);

This is a void function, so it cannot return anything.

>  }
>
>  int pm_qos_sysfs_add_resume_latency(struct device *dev)
> --