Re: changing URB allocation API

Am Freitag, 6. Juli 2007 schrieb Alan Stern:
> On Fri, 6 Jul 2007, Oliver Neukum wrote:
> 
> > Hi,
> > 
> > I tried switching our allocation APIs to:
> > 
> > struct urb *usb_alloc_urb(struct usb_host_endpoint *ep, size_t alloc_length, gfp_t mem_flags);
> > struct urb *usb_alloc_iso_urb(struct usb_host_endpoint *ep, unsigned int iso_packets, gfp_t mem_flags);
> > 
> > Unfortunately during initialisation ep->ep_dev turns out to be NULL.
> > Should I change the allocator or the initialisation?
> 
> That's a real problem.  During initial enumeration the usb_device 
> hasn't been registered yet, so the ep_device hasn't been created.
> 
> One possibility is to add yet another allocator:
> 
> struct urb *usb_alloc_ep0_urb(struct usb_device *udev, size_t alloc_length, 
> 		gfp_t mem_flags);

Very well. Given the call chain this means changing the API of the
usb_*_msg() calls to pass in an URB. If I do that I'll preallocate an URB
per device for usbcore's calls to ep0 to make sure we won't face ENOMEM
in some very awkward situations.

> This could have an additional extra use, since it could leave space for 
> the setup packet at the end of the URB (rounded up to the next cache 
> line).

That collides with the HCD allocating the URB, or it means also changing
the HCD interface and adding a method just for this.

	Regards
		Oliver

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