Re: [PATCH v3] usb: gadget: f_midi: Add checking if it need align buffer's size to an ep's maxpacketsize

[Baolin Wang]

Hi Felipe,

On 26 July 2016 at 19:06, Felipe Ferreri Tonello <eu@xxxxxxxxxxxxxxxxx> wrote:
> Hi Baolin,
>
> Sorry for not replying for previous emails because for some reason these
> emails were archived. :(
>
> On 12/07/16 10:01, Baolin Wang wrote:
>> 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@xxxxxxxxxx>
>> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>> ---
>> Changelog:
>> v2:
>>  - Simplify the method to get buffer length.
>> v1:
>>  - Remove the in_ep modification.
>>  - Remove max_t() function.
>>
>>  drivers/usb/gadget/function/f_midi.c |   11 +++++++----
>>  1 file changed, 7 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/usb/gadget/function/f_midi.c b/drivers/usb/gadget/function/f_midi.c
>> index 58fc199..3486941 100644
>> --- a/drivers/usb/gadget/function/f_midi.c
>> +++ b/drivers/usb/gadget/function/f_midi.c
>> @@ -359,10 +359,13 @@ 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;
>> +             unsigned length;
>> +
>> +             length = usb_ep_align_maybe(midi->gadget, midi->out_ep,
>> +                                         midi->buflen);
>> +
>> +             req = midi_alloc_ep_req(midi->out_ep, length);
>>               if (req == NULL)
>>                       return -ENOMEM;
>>
>>
>
> Yes, as mentioned before, my intent was to align the size otherwise an
> actual nasty bug happens.
>
> I have two problems with this approach:
> * usb_ep_align_maybe() has a bug that it doesn't convert wMaxPacketSize
> endianness to the CPU. See my patch on that[1] subject. Also this

Yes, you are right, I missed that.

> function uses round_up which expects x and y to be a power of 2, is that
> a feasible assumption?

I suppose it only expects y is a power of 2.

> * If the gadget driver doesn't support quirk_ep_out_aligned_size,
> usb_ep_align_maybe() can potentially return a len < wMaxPacketSize.
> Basically causing a regression.

Okay.

>
> I believe we should protect this bad behavior on alloc_ep_req() in
> drivers/usb/gadget/u_f.c by forcing align the size if the endpoint in
> subject is OUT.
>
> [1] [PATCH 1/4] usb: gadget: f_midi: fixed endianness when using
> wMaxPacketSize: https://lkml.org/lkml/2016/7/25/1028


-- 
Baolin.wang
Best Regards