Re: [PATCH] usb: storage: fix runtime pm issue in usb_stor_probe2

[Heiner Kallweit <hkallweit1-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Am 03.08.2016 um 23:25 schrieb Alan Stern:
> On Wed, 3 Aug 2016, Heiner Kallweit wrote:
> 
>> Since commit 71723f95463d "PM / runtime: print error when activating a
>> child to unactive parent" I see the following error message:
>>
>> scsi host2: usb-storage 1-3:1.0
>> scsi host2: runtime PM trying to activate child device host2 but parent
>> 	    (1-3:1.0) is not active
>>
>> Digging into it it seems to be related to the problem described in the
>> commit message for cd998ded5c12 "i2c: designware: Prevent runtime
>> suspend during adapter registration" as scsi_add_host also calls
>> device_add and after the call to device_add the parent device is
>> suspended.
>>
>> Fix this by using the approach from the mentioned commit and getting
>> the runtime pm reference before calling scsi_add_host.
> 
> Acked-by: Alan Stern <stern-nwvwT67g6+6dFdvTe/nMLpVzexx5G7lz@public.gmane.org>
> 
> There's nothing wrong with this patch; it's a worthwhile thing to do 
> because it can prevent an unnecessary runtime-suspend/resume cycle.
> 
> Still, it looks like the real problem here may lie in
> drivers/scsi/hosts.c.  Commit bc4f24014de5 ("[SCSI] implement runtime
> Power Management") added a call to pm_runtime_set_active() in
> scsi_add_host_with_dma() _after_ device_add() instead of _before_.
> 
> If that were changed, this problem would not have occurred.
> 
In parallel to this patch I sent another one to address exactly the
ordering issue in scsi_add_host_with_dma you mention.
The other patch went to Martin and the SCSI mailing list only, sorry.
I'll forward it to you for review.

Heiner

> Alan Stern
> 
> 

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