Re: [RFC][PATCH v2 06/13] usb: hcd: Add hcd add/remove functions for OTG use

[Roger Quadros]

On 20/04/15 16:56, Alan Stern wrote:
> On Mon, 20 Apr 2015, Roger Quadros wrote:
> 
>>> I don't understand this.  Why do you want to defer the add/remove if 
>>> the device is OTG?  Don't host controller drivers expect these things 
>>> to execute synchronously?
>>
>> Sorry for the wrong information. We actually defer only the add as the
>> OTG state machine might not yet be in Host ready mode.
>> The remove is always synchronous and we ensure that the HCD is removed
>> when usb_otg_unregister_hcd() returns.
> 
> That's okay then, but it does leave one potential hole.  What happens 
> if usb_add_hcd() is deferred for so long that usb_remove_hcd() gets 
> called before the add can complete?

We keep track of the HCD state in the OTG state machine and if it was not
yet added then _usb_remove_hcd() is not called during usb_otg_unregister_hcd()
in the usb_remove_hcd() call.

cheers,
-roger

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