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.
Alan Stern
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