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

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Date:	Tue, 8 Sep 2015 10:34:51 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Roger Quadros <rogerq@...com>
cc:	Peter Chen <peter.chen@...escale.com>, <balbi@...com>,
	<gregkh@...uxfoundation.org>, <dan.j.williams@...el.com>,
	<jun.li@...escale.com>, <mathias.nyman@...ux.intel.com>,
	<tony@...mide.com>, <Joao.Pinto@...opsys.com>,
	<abrestic@...omium.org>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v4 07/13] usb: otg: add OTG core

On Tue, 8 Sep 2015, 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.

This seems a lot like something Peter and I discussed recently.  See

	http://marc.info/?l=linux-usb&m=143977568021328&w=2

and the following messages in that thread.

Alan Stern


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