linux-kernel - Re: [PATCH v2 2/3] usb: gadget: f_midi: free usb request when done

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Date:	Fri, 25 Sep 2015 10:22:17 +0100
From:	Felipe Tonello <eu@...ipetonello.com>
To:	Peter Chen <peter.chen@...escale.com>
Cc:	USB list <linux-usb@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Felipe Balbi <balbi@...com>,
	Andrzej Pietrasiewicz <andrzej.p@...sung.com>
Subject: Re: [PATCH v2 2/3] usb: gadget: f_midi: free usb request when done

Hi Peter,

On Thu, Sep 24, 2015 at 2:38 AM, Peter Chen <peter.chen@...escale.com> wrote:
> On Wed, Sep 23, 2015 at 01:01:44PM +0100, Felipe F. Tonello wrote:
>> req->actual == req->length means that there is no data left to enqueue,
>> so free the request.
>>
>> Signed-off-by: Felipe F. Tonello <eu@...ipetonello.com>
>> ---
>>
>> Changes in v2:
>>  * Re enqueue not fully completed requests, instead of read ALSA buffers.
>>
>>  drivers/usb/gadget/function/f_midi.c | 10 ++++++----
>>  1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>> index edb84ca..62356cf 100644
>> --- a/drivers/usb/gadget/function/f_midi.c
>> +++ b/drivers/usb/gadget/function/f_midi.c
>> @@ -256,10 +256,12 @@ f_midi_complete(struct usb_ep *ep, struct usb_request *req)
>>                       /* We received stuff. req is queued again, below */
>>                       f_midi_handle_out_data(ep, req);
>>               } else if (ep == midi->in_ep) {
>> -                     /* Our transmit completed. See if there's more to go.
>> -                      * f_midi_transmit eats req, don't queue it again. */
>> -                     f_midi_transmit(midi, req);
>> -                     return;
>> +                     /* Our transmit completed. If there is no more to go,
>> +                        don't queue it again. */
>> +                     if (req->actual == req->length) {
>> +                             free_ep_req(ep, req);
>> +                             return;
>> +                     }
>
> I find f_midi_transmit will judge if there are more data, if without
> data, it will free the request.

No. Transmit is called when ALSA trigger is called (whenever
snd_*_read() snd_*_write() is called).

The current code is not crashing anything, but I believe it is just
wrong. It can cause potential problems in future if one is not careful
when doing changes to it.

I would like to send a v3 with free_ep_req().

Felipe

>
> Besides, does one trigger only do one transfer? Sorry, I can't make my
> aplaymidi to receive data, probably due to hardware without midi
> support?
>
> root@...6qpsabreauto:~# aplaymidi
> ALSA lib
> /var/lib/jenkins/workspace/fido-3.14.28-X11-consolidated_new/temp_build_dir/build_all/tmp/work/cortexa9hf-vfp-neon-mx6qdl-poky-linux-gnueabi/alsa-lib/1.0.28-r0/alsa-lib-1.0.28/src/seq/seq_hw.c:457:(snd_seq_hw_open)
> open /dev/snd/seq failed: No such file or directory
> Cannot open sequencer - No such file or directory
>
> --
>
> Best Regards,
> Peter Chen
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