linux-kernel - Re: [PATCH v4 1/7] usb: gadget: f_midi: Transmit data only when IN ep is enabled

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Date:	Tue, 27 Oct 2015 07:41:51 +0100
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	Felipe Tonello <eu@...ipetonello.com>,
	Robert Baldyga <r.baldyga@...kerion.com>
Cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrzej Pietrasiewicz <andrzej.p@...sung.com>,
	Clemens Ladisch <clemens@...isch.de>
Subject: Re: [PATCH v4 1/7] usb: gadget: f_midi: Transmit data only when IN ep
 is enabled

On 10/26/2015 11:49 PM, Felipe Tonello wrote:
> Hi Robert,
> 
> On Mon, Oct 26, 2015 at 10:13 PM, Robert Baldyga
> <r.baldyga@...kerion.com> wrote:
>> Hi Felipe,
>>
>> On 10/26/2015 05:55 PM, Felipe F. Tonello wrote:
>>> This makes sure f_midi doesn't try to enqueue data when the IN endpoint is
>>> disabled, ie, USB cable is disconnected.
>>>
>>> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>>> ---
>>>  drivers/usb/gadget/function/f_midi.c | 7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>>> index edb84ca..e08f365 100644
>>> --- a/drivers/usb/gadget/function/f_midi.c
>>> +++ b/drivers/usb/gadget/function/f_midi.c
>>> @@ -87,6 +87,7 @@ struct f_midi {
>>>       int index;
>>>       char *id;
>>>       unsigned int buflen, qlen;
>>> +     bool in_ep_enabled;
>>
>> It's not necessary, you can use ep->enabled flag instead.
> 
> There is no such flag in usb_ep struct[1].
> 
> [1] http://lxr.free-electrons.com/source/include/linux/usb/gadget.h#L170

It's already in next branch of Felipe Balbi's tree.

Look here:
https://git.kernel.org/cgit/linux/kernel/git/balbi/usb.git/

Best regards,
Robert

> 
>>
>>>  };
>>>
>>>  static inline struct f_midi *func_to_midi(struct usb_function *f)
>>> @@ -332,6 +333,7 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>>       err = f_midi_start_ep(midi, f, midi->in_ep);
>>>       if (err)
>>>               return err;
>>> +     midi->in_ep_enabled = true;
>>>
>>>       err = f_midi_start_ep(midi, f, midi->out_ep);
>>>       if (err)
>>> @@ -387,6 +389,8 @@ static void f_midi_disable(struct usb_function *f)
>>>        */
>>>       usb_ep_disable(midi->in_ep);
>>>       usb_ep_disable(midi->out_ep);
>>> +
>>> +     midi->in_ep_enabled = false;
>>>  }
>>>
>>>  static int f_midi_snd_free(struct snd_device *device)
>>> @@ -543,7 +547,7 @@ static void f_midi_transmit(struct f_midi *midi, struct usb_request *req)
>>>               }
>>>       }
>>>
>>> -     if (req->length > 0) {
>>> +     if (req->length > 0 && midi->in_ep_enabled) {
>>
>> You should rather test it at the beginning of this function. Or, even
>> better, when tasklet is scheduled, because tasklet is the only way this
>> function can be called when endpoints are disabled.
> 
> Not in this case, because this function needs to consume the triggered
> data from ALSA, otherwise a timeout will happen (which is worse).
> Of course this is not the best solution, but it is an incremental improvement.
> 
> Patch 7 has the proper solution, which checks this flag at the
> beginning of the function as expected. Also, it is more optimal
> because it drops all substreams buffers, instead of copying it.
> 
>>
>>>               int err;
>>>
>>>               err = usb_ep_queue(ep, req, GFP_ATOMIC);
>>> @@ -1158,6 +1162,7 @@ static struct usb_function *f_midi_alloc(struct usb_function_instance *fi)
>>>       midi->index = opts->index;
>>>       midi->buflen = opts->buflen;
>>>       midi->qlen = opts->qlen;
>>> +     midi->in_ep_enabled = false;
>>>       ++opts->refcnt;
>>>       mutex_unlock(&opts->lock);
>>>
>>>
>>
> 
> Felipe
> --
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