Re: [linux-pm] rtl8187 usb wifi adaptor causes suspend hang

[Alan Jenkins <alan-jenkins@tuffmail.co.uk>]

Alan Stern wrote:
> On Tue, 30 Dec 2008, Bob Copeland wrote:
>
>   
>> On Tue, Dec 30, 2008 at 10:45 AM, Alan Stern <stern@rowland.harvard.edu> wrote:
>>     
>>>> Is it possible to fix this without suspend support in mac80211?  If not,
>>>> I vote we change rtl8187 (and zd_usb) to prevent suspend.  I.e. set USB
>>>> suspend callbacks which return an error.
>>>>         
>> Alan J:
>>
>> Are you using 'echo -n mem > /sys/power/state' directly to do suspend,
>> or hitting the power button?  I'm guessing we shouldn't be calling
>> disconnect() when suspending.
>>
>>     
>>> It certainly should be possible to fix this.  For instance, why
>>> unregister anything during suspend?  If ieee80211_unregister_hw()
>>> weren't called then this problem would go away, right?
>>>       
>> Yes, we shouldn't need to.
>>
>> But it's not the suspend() callback that's getting called (the driver
>> doesn't have one) but disconnect, which unregisters itself from the
>> upper layers.  I just read the stuff in Documentation/usb but admit I
>> don't fully get the rules.  AIUI, without suspend/resume callbacks,
>> disconnect will sometimes get called on resume?  But the original
>> email is a hang at suspend time?
>>     
>
> This explains the problem.  Yes, drivers that don't have a suspend or
> resume method will have their disconnect method called when a system
> suspend occurs.
>
> An easy way to prevent this is to add empty suspend and resume methods 
> (and a resume_reset method too).
>   

That won't fix hibernation though.  The disconnect method can still get
called in resume from hibernation, before the workqueue gets unfrozen. 
To be honest, I'm far more interested in suspend-to-disk than
suspend-to-ram.

> Alternatively, you can allow the disconnect to occur.  If the workqueue 
> weren't freezable then the problem would be solved.  Which leads to the 
> question: Why have a freezable workqueue if there's no suspend/resume 
> support in the driver?
>