On 11/05/2013 06:50 AM, Alan Stern wrote:
> On Mon, 4 Nov 2013, David Cohen wrote:
>
>> Due to USB controllers may have different restrictions, usb gadget layer
>> needs to provide a generic way to inform gadget functions to complain
>> with non-standard requirements.
>>
>> This patch adds 'quirk_ep_out_aligned_size' field to struct usb_gadget
>> to inform when controller's epout requires buffer size to be aligned to
>> MaxPacketSize. A helper is also provided to align buffer size when
>> necessary.
>>
>> Signed-off-by: David Cohen <david.a.cohen@xxxxxxxxxxxxxxx>
>> ---
>> include/linux/usb/gadget.h | 19 +++++++++++++++++++
>> 1 file changed, 19 insertions(+)
>>
>> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
>> index 23b3bfd0a842..260d972489bd 100644
>> --- a/include/linux/usb/gadget.h
>> +++ b/include/linux/usb/gadget.h
>> @@ -442,6 +442,22 @@ static inline void usb_ep_fifo_flush(struct usb_ep *ep)
>> }
>>
>>
>> +static inline size_t usb_ep_align_maxpacketsize(struct usb_ep *ep, size_t len)
>> +{
>> + int aligned;
>> +
>> + if (ep->desc->bmAttributes & USB_ENDPOINT_XFER_INT)
>> + /*
>> + * Interrupt eps don't need max packet size to be power of 2,
>> + * so can't use cheap IS_ALIGNED() macro.
>> + */
>> + aligned = !(len % ep->desc->wMaxPacketSize);
>> + else
>> + aligned = IS_ALIGNED(len, ep->desc->wMaxPacketSize);
>
> This isn't on a hot path, and I suspect that the extra "if" will
> require nearly as much time as you save by not doing the division. You
> might as well always use the % operation.
Perhaps if I use unlikely() on 'if' condition instead?
Anyway I'll double check the costs of if + IS_ALIGNED vs modulo.
Br, David
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