linux-kernel - Re: [PATCH] usb: gadget: f_midi: Add checking if it need align buffer's size to an ep's maxpacketsize

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Date:	Mon, 11 Jul 2016 10:22:03 +0800
From:	Baolin Wang <baolin.wang@...aro.org>
To:	Felipe Balbi <balbi@...nel.org>
Cc:	Greg KH <gregkh@...uxfoundation.org>, eu@...ipetonello.com,
	Michal Nazarewicz <mina86@...a86.com>, r.baldyga@...sung.com,
	dan.carpenter@...cle.com, USB <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] usb: gadget: f_midi: Add checking if it need align
 buffer's size to an ep's maxpacketsize

On 8 July 2016 at 21:21, Felipe Balbi <balbi@...nel.org> wrote:
>
> Hi,
>
> Baolin Wang <baolin.wang@...aro.org> writes:
>> Some gadget device (such as dwc3 gadget) requires quirk_ep_out_aligned_size
>> attribute, which means it need to align the request buffer's size to an ep's
>> maxpacketsize.
>>
>> Thus we add usb_ep_align_maybe() function to check if it is need to align
>> the request buffer's size to an ep's maxpacketsize.
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...aro.org>
>> ---
>>  drivers/usb/gadget/function/f_midi.c |   18 +++++++++++-------
>>  1 file changed, 11 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>> index 58fc199..2e3f11e 100644
>> --- a/drivers/usb/gadget/function/f_midi.c
>> +++ b/drivers/usb/gadget/function/f_midi.c
>> @@ -328,7 +328,7 @@ static int f_midi_start_ep(struct f_midi *midi,
>>  static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>  {
>>       struct f_midi *midi = func_to_midi(f);
>> -     unsigned i;
>> +     unsigned i, length;
>>       int err;
>>
>>       /* we only set alt for MIDIStreaming interface */
>> @@ -345,9 +345,11 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>
>>       /* pre-allocate write usb requests to use on f_midi_transmit. */
>>       while (kfifo_avail(&midi->in_req_fifo)) {
>> -             struct usb_request *req =
>> -                     midi_alloc_ep_req(midi->in_ep, midi->buflen);
>> +             struct usb_request *req;
>>
>> +             length = usb_ep_align_maybe(midi->gadget, midi->in_ep,
>> +                                         midi->buflen);
>
> this is not needed for in_ep, only out_ep, right?

Yes. You are right.

>
>> +             req = midi_alloc_ep_req(midi->in_ep, length);
>>               if (req == NULL)
>>                       return -ENOMEM;
>>
>> @@ -359,10 +361,12 @@ static int f_midi_set_alt(struct usb_function *f, unsigned intf, unsigned alt)
>>
>>       /* allocate a bunch of read buffers and queue them all at once. */
>>       for (i = 0; i < midi->qlen && err == 0; i++) {
>> -             struct usb_request *req =
>> -                     midi_alloc_ep_req(midi->out_ep,
>> -                             max_t(unsigned, midi->buflen,
>> -                                     bulk_out_desc.wMaxPacketSize));
>> +             struct usb_request *req;
>> +
>> +             length = usb_ep_align_maybe(midi->gadget, midi->out_ep,
>> +                                         midi->buflen);
>
> after calling usb_ep_align_maybe()...
>
>> +             req = midi_alloc_ep_req(midi->out_ep,
>> +                     max_t(unsigned, length, bulk_out_desc.wMaxPacketSize));
>
> ... max_t() is pointless. length will *always* >= wMaxPacketSize.

It is not. If the gadget device dose not require
quirk_ep_out_aligned_size, then the lengh may be <= wMaxPacketSize.

-- 
Baolin.wang
Best Regards