Re: [PATCH v5 2/5] usb: gadget: add quirk_ep_out_aligned_size fieldto struct usb_gadget

[David Cohen]

On 11/11/2013 03:55 PM, Michal Nazarewicz wrote:
> On Mon, Nov 11 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>
> > Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
>
> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>
> > ---
> >
> > Michal,
> >
> > I added prefix 'usb: f_fs: ' to patch's subject. I did not add 'usb: gadget:
> > f_fs' due to it would be too long.
> >
> >
> >   include/linux/usb/gadget.h | 16 ++++++++++++++++
> >   1 file changed, 16 insertions(+)
> >
> > diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
> > index 23b3bfd0a842..41e8834af57d 100644
> > --- a/include/linux/usb/gadget.h
> > +++ b/include/linux/usb/gadget.h
> > @@ -441,6 +441,19 @@ static inline void usb_ep_fifo_flush(struct usb_ep *ep)
> >   		ep->ops->fifo_flush(ep);
> >   }
> >
> > +/**
> > + * usb_ep_align_maxpacketsize - returns @len aligned to ep's maxpacketsize
> > + * @ep: the endpoint whose maxpacketsize is used to align @len
> > + * @len: buffer size's length to align to @ep's maxpacketsize
> > + *
> > + * This helper is used in case it's required for any reason to align buffer's
> > + * size to an ep's maxpacketsize.
> > + */
> > +static inline size_t usb_ep_align_maxpacketsize(struct usb_ep *ep, size_t len)
> > +{
> > +	return round_up(len, (size_t)ep->desc->wMaxPacketSize);
> > +}
> > +
>
> Come to think of it, perhaps even better helper would be:
>
> static inline size_t usb_ep_align_maybe(
> 	struct usb_gadget *gadget, struct usb_ep *ep, size_t len) {
> 	return gadget->quir_ep_out_aligned_size ?
> 		round_up(len, (size_t)ep->desc->wMaxPacketSize) : len;
> }

The CPU time to check unsigned:1 and possibly jump is about the same as
round_up() itself. For readability matters, we can round_up() directly.

Br, David
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