Re: [PATCH v4 07/13] usb: otg: add OTG core

[Peter Chen <peter.chen@freescale.com>]

On Wed, Sep 09, 2015 at 12:08:10PM +0300, Roger Quadros wrote:
> On 09/09/15 05:21, Peter Chen wrote:
> > On Tue, Sep 08, 2015 at 03:25:25PM +0300, Roger Quadros wrote:
> >>
> >>
> >> On 08/09/15 11:31, Peter Chen wrote:
> >>> On Mon, Sep 07, 2015 at 01:23:01PM +0300, Roger Quadros wrote:
> >>>> On 07/09/15 04:23, Peter Chen wrote:
> >>>>> On Mon, Aug 24, 2015 at 04:21:18PM +0300, Roger Quadros wrote:
> >>>>>> + * This is used by the USB Host stack to register the Host controller
> >>>>>> + * to the OTG core. Host controller must not be started by the
> >>>>>> + * caller as it is left upto the OTG state machine to do so.
> >>>>>> + *
> >>>>>> + * Returns: 0 on success, error value otherwise.
> >>>>>> + */
> >>>>>> +int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
> >>>>>> +			 unsigned long irqflags, struct otg_hcd_ops *ops)
> >>>>>> +{
> >>>>>> +	struct usb_otg *otgd;
> >>>>>> +	struct device *hcd_dev = hcd->self.controller;
> >>>>>> +	struct device *otg_dev = usb_otg_get_device(hcd_dev);
> >>>>>> +
> >>>>>
> >>>>> One big problem here is: there are two designs for current (IP) driver
> >>>>> code, one creates dedicated hcd device as roothub's parent, like dwc3.
> >>>>> Another one doesn't do this, roothub's parent is core device (or otg device
> >>>>> in your patch), like chipidea and dwc2.
> >>>>>
> >>>>> Then, otg_dev will be glue layer device for chipidea after that.
> >>>>
> >>>> OK. Let's add a way for the otg controller driver to provide the host and gadget
> >>>> information to the otg core for such devices like chipidea and dwc2.
> >>>>
> >>>
> >>> Roger, not only chipidea and dwc2, I think the musb uses the same
> >>> hierarchy. If the host, device, and otg share the same register
> >>> region, host part can't be a platform driver since we don't want
> >>> to remap the same register region again.
> >>>
> >>> So, in the design, we may need to consider both situations, one
> >>> is otg/host/device has its own register region, and host is a
> >>> separate platform device (A), the other is three parts share the
> >>> same register region, there is only one platform driver (B).
> >>>
> >>> A:
> >>>
> >>> 			IP core device 
> >>> 			    |
> >>> 			    |
> >>> 		      |-----|-----|
> >>> 		      gadget   host platform device	
> >>> 		      		|
> >>> 				roothub
> >>>
> >>> B:
> >>>
> >>> 			IP core device
> >>> 			    |
> >>> 			    |
> >>> 		      |-----|-----|
> >>> 		      gadget   	 roothub
> >>> 		      		
> >>>
> >>>> This API must be called before the hcd/gadget-driver is added so that the otg
> >>>> core knows it's linked to an OTG controller.
> >>>>
> >>>> Any better idea?
> >>>>
> >>>
> >>> A flag stands for this hcd controller is the same with otg controller
> >>> can be used, this flag can be stored at struct usb_otg_config.
> >>
> >> What if there is another architecture like so?
> >>
> >> C:
> >> 			[Parent]
> >> 			   |
> >> 			   |
> >> 		|------------------|--------------|
> >> 	[OTG core]		[gadget]	[host]
> >>
> >> We need a more flexible mechanism to link the gadget and
> >> host device to the otg core for non DT case.
> >>
> >> How about adding struct usb_otg parameter to usb_otg_register_hcd()?
> >>
> >> e.g.
> >> int usb_otg_register_hcd(struct usb_otg *otg, struct usb_hcd *hcd, ..)
> >>
> >> If otg is NULL it will try DT otg-controller property or parent to
> >> get the otg controller.
> > 
> > How usb_otg_register_hcd get struct usb_otg, from where?
> 
> This only works when the parent driver creating the hcd has registered the
> otg controller too.
> 

Sorry? So we need to find another way to solve this issue, right?

> > 
> >>
> >>>
> >>> Peter
> >>>
> >>> P.S: I still read your code, I find not all APIs in this file are used
> >>> in your dwc3 example. 
> >>
> >> Which ones? The ones for registering/unregistered host/gadget are used
> >> by hcd/udc core as part of usb_add/remove_hcd() and
> >> udc_bind_to_driver()/usb_gadget_remove_driver()
> >>
> > 
> > Ok, now I understand your design, usb_create_hcd must be called before
> > the fsm kicks off. The call flow like below:
> > 
> > usb_otg_register->usb_create_hcd->usb_add_hcd->usb_otg_register_hcd->
> > usb_otg_start_host->usb_otg_add_hcd
> 
> Actually these are the discrete steps
> - usb_otg_register
> - usb_create_hcd
> - usb_add_hcd->usb_otg_register_hcd  (HCD is not really added till FSM in host role)
> 
> Above 3 are prerequisite for FSM to start in addition to gadget controller and
> driver being ready.
> 
> When FSM enters in host role
> - usb_otg_start_host(true)->usb_otg_add_hcd (Now HCD is added)
> 
> When FSM exits host role
> - usb_otg_start_host(false)->usb_otg_remove_hcd (Now HCD is removed, but not unregistered)
> 
> If HCD hardware really goes away
> - usb_remove_hcd->usb_otg_unregister_hcd (Now FSM stops as host resource not available)
> 
> > 
> > We need to make some changes to let chipidea work since usb_create_hcd
> > is included at host->start.
> > 
> 
> Yes, you just need to do the usb_add_hcd() in probe
> and usb_otg_start_host() during role switch.
> 

Thanks.

-- 

Best Regards,
Peter Chen