Re: [PATCH 0/3] usb: gadget: uvc: allocate requests based on frame interval length and buffersize

Alan Stern
2024-05-22T14:50:33Z

On Wed, May 22, 2024 at 01:41:42AM +0000, Thinh Nguyen wrote:
> On Wed, May 22, 2024, Michael Grzeschik wrote:
> > On Fri, May 17, 2024 at 01:44:05AM +0000, Thinh Nguyen wrote:
> > > For isoc endpoint IN, yes. If the host requests for isoc data IN while
> > > no TRB is prepared, then the controller will automatically send 0-length
> > > packet respond.
> >
> > Perfect! This will help a lot and will make active queueing of own
> > zero-length requests run unnecessary.
>
> Yes, if we rely on the current start/stop isoc transfer scheme for UVC,
> then this will work.

You shouldn't rely on this behavior. Other device controllers might not
behave this way; they might send no packet at all to the host (causing a
USB protocol error) instead of sending a zero-length packet.

On the other hand, it may not make any difference. The host's UVC
driver most likely won't care about the difference between no packet and
a 0-length packet. :-)

Alan Stern