linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq

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Message-ID: <871szftmyi.fsf@linux.intel.com>
Date:   Mon, 17 Oct 2016 11:10:45 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Baolin Wang <baolin.wang@...aro.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Mark Brown <broonie@...nel.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Wait for end transfer complete before free irq


Hi,

(I have added you to another thread which is where we'll be collecting
discussion about this, however ...)

Alan Stern <stern@...land.harvard.edu> writes:
> On Fri, 14 Oct 2016, Felipe Balbi wrote:
>
>> argh, we have nested spinlocks :-( Well, we shouldn't call
>> usb_ep_disable() with locks held AFAICR. So the following should be
>> enough:
>> 
>> diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
>> index 919d7d1b611c..2e9359c58eb9 100644
>> --- a/drivers/usb/gadget/composite.c
>> +++ b/drivers/usb/gadget/composite.c
>> @@ -732,8 +732,10 @@ static void reset_config(struct usb_composite_dev *cdev)
>>         DBG(cdev, "reset config\n");
>>  
>>         list_for_each_entry(f, &cdev->config->functions, list) {
>> +               spin_unlock_irq(&cdev->lock);
>>                 if (f->disable)
>>                         f->disable(f);
>> +               spin_lock_irq(&cdev->lock);
>>  
>>                 bitmap_zero(f->endpoints, 32);
>>         }
>> 
>> Alan, do you remember if we have a requirement for not holding locks
>> when calling usb_ep_disable()? I can't find Documentation about it, but
>> history shows me that usb_ep_disable() was called without locks and IRQs
>> enabled. Do you think we should update documentation about this?
>
> I don't think there is any requirement for interrupts to be enabled 
> when usb_ep_disable() runs.  At least, a quick check shows that both 
> net2280 and dummy-hcd use spin_lock_irqsave() rather than spin_lock() 
> in their disable routines.
>
> Holding locks is a different story.  It should be okay for a gadget 
> driver to hold one of its own locks when disabling an endpoint (which 
> means that the gadget's disable routine shouldn't wait for a concurrent 
> giveback to finish), but we might want to avoid holding a lock in the 
> composite core.  Although even that might be okay -- I can't think of 
> any reason why a udc driver would need to call back into the composite 
> core while disabling an endpoint.  It should be a pretty self-contained 
> operation.

True, but how do we handle controllers which need to wait for an
interrupt in order to cancel a transfer? Maybe we should change the
calling context of usb_ep_disable() so that it _must_ be called with
IRQs enabled?

-- 
balbi

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