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

[Felipe Tonello]

Hi Robert,

On Mon, Oct 26, 2015 at 10:13 PM, Robert Baldyga
<r.baldyga@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxx>
>> ---
>>  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

>
>>  };
>>
>>  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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