linux-kernel - Re: Calling device_init_wakeup() on driver removal

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Message-ID: <d50f9cf4-99e8-b95e-dc6c-317b06d75cdc@roeck-us.net>
Date:   Sun, 15 Jan 2017 07:23:28 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Calling device_init_wakeup() on driver removal

On 01/15/2017 06:49 AM, Rafael J. Wysocki wrote:
> On Saturday, January 14, 2017 08:46:05 PM Guenter Roeck wrote:
>> Hi folks,
>
> Hi,
>
>> while looking through driver initialization and removal functions, I noticed that many drivers
>> call device_init_wakeup(dev, false) in the removal function. Given that the driver is about
>> to be removed, that doesn't make much sense to me, especially since device_wakeup_disable()
>> is called from device_pm_remove() anyway.
>>
>> Is it safe to assume that all those calls can be removed, or is there a possible reason for
>> keeping them around ?
>
> Removing them automatically might break things, because device_init_wakeup(dev, false)
> also clears the power.can_wakeup flag and removes the "wakeup" attribute from sysfs.
>

I had the same concern, but I concluded that the wakeup attribute should be removed
automatically, since it is added with sysfs_merge_group(), and the matching unmerge call
is also made in dpm_sysfs_remove(). power.can_wakeup is part of the device structure,
which is in the process of being removed, so I am not sure I understand how that can be
problematic.

> I guess they could be removed safely in the majority of cases, though.

How would one decide if it is needed ? I see some drivers call it on remove, but others
don't. I don't see a clear pattern; unless I am missing something, it seems to be
more or less random.

Thanks,
Guenter