[U-Boot] [PATCH 1/3] usb: ci_udc: Fix set address to work with older controllers

[Alban Bedel]

On Tue, 24 Feb 2015 10:00:43 -0700
Stephen Warren <swarren at wwwdotorg.org> wrote:

> On 02/24/2015 09:44 AM, Alban Bedel wrote:
> > Older controllers don't implement "Device Address Advance" which allow
> > to pass the device address to the controller when it is received.
> > To support such controller we need to store the requested address and
> > only apply it after the next IN transfer completed on EP0.
> 
> > diff --git a/drivers/usb/gadget/ci_udc.c b/drivers/usb/gadget/ci_udc.c
> 
> >   	case SETUP(USB_RECIP_DEVICE, USB_REQ_SET_ADDRESS):
> > -		/*
> > -		 * write address delayed (will take effect
> > -		 * after the next IN txn)
> > -		 */
> > -		writel((r.wValue << 25) | (1 << 24), &udc->devaddr);
> > +		/* The device address must be updated after the next IN
> > +		 * request completed */
> > +		controller.set_address = r.wValue;
> 
> Presumably, bit 24 is the "device address advance" feature?

Yes, bit 24 is the "device address advance" feature

> I'd prefer it if new controllers used the existing code, but we deferred 
> the write only for older controllers that don't support "device address 
> advance". That reduces the possibility of regressions on controller HW 
> that's already working. Presumably, there is some advantage using the 
> new feature, rather than deferring the address change manually, e.g. it 
> solves some race condition?

I'm no USB expert, but AFAIU it is only a convenience to make the
driver code simpler. I though that having less code path and ifdef
would make the whole thing easier to maintain. However if that is
preferred I can implement it as you suggested.

Alban

PS: Sorry for the double mail Stephen, I accidentally used the wrong
    reply button.
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