[v5,1/2] usb/gadget: Add an EP dispose() callback for EP lifetime tracking

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2018-03-16 at 13:02 +0200, Felipe Balbi wrote:
> Hi,
> 
> Benjamin Herrenschmidt <benh@kernel.crashing.org> writes:
> > Some UDC may want to allocate endpoints dynamically, either because
> > the HW supports an arbitrary large number or because (like the Aspeed
> > BMC SoCs), the pool of HW endpoints is shared between multiple gadgets.
> > 
> > The allocation side can be done rather easily using the existing
> > match_ep() UDC hook.
> > 
> > However we have no good place to "free" them.
> > 
> > This implements a "simple" variant of this, which calls an EP dispose
> > callback on all EPs associated with a gadget when the composite device
> > gets unbound.
> > 
> > This is required by my upcoming Aspeed vHub driver.
> > 
> > Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > ---
> >  drivers/usb/gadget/composite.c | 8 ++++++++
> >  include/linux/usb/gadget.h     | 1 +
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
> > index 77c7ecca816a..ec99c9cfc1a2 100644
> > --- a/drivers/usb/gadget/composite.c
> > +++ b/drivers/usb/gadget/composite.c
> > @@ -2172,6 +2172,7 @@ int composite_os_desc_req_prepare(struct usb_composite_dev *cdev,
> >  void composite_dev_cleanup(struct usb_composite_dev *cdev)
> >  {
> >  	struct usb_gadget_string_container *uc, *tmp;
> > +	struct usb_ep			   *ep, *tmp_ep;
> >  
> >  	list_for_each_entry_safe(uc, tmp, &cdev->gstrings, list) {
> >  		list_del(&uc->list);
> > @@ -2193,6 +2194,13 @@ void composite_dev_cleanup(struct usb_composite_dev *cdev)
> >  	}
> >  	cdev->next_string_id = 0;
> >  	device_remove_file(&cdev->gadget->dev, &dev_attr_suspended);
> > +
> > +	/* Dispose EPs if the UDC driver tracks lifetime */
> > +	list_for_each_entry_safe(ep, tmp_ep,
> > +				 &cdev->gadget->ep_list, ep_list) {
> 
> do you really need this to be safe? You don't seem to be modifying
> ep_list here.

Yes, ep->dispose() may do just that. In my Aspeed implementation in
fact that's pretty much the first thing it does.

IE, I'm returning all the endpoints to the common pool, thus taking
them out of the gadget EP list.

That said, there could be other reasons why a driver might want to know
about disposal without actually taking all the EPs back (for example a
driver could have some dedicated EPs and some in a pool) so I prefer
the list_del remaining in the back-end.

Cheers,
Ben.
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