linux-kernel - RE: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface

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Date:	Tue, 10 May 2016 08:03:20 +0000
From:	Jun Li <jun.li@....com>
To:	Roger Quadros <rogerq@...com>, Peter Chen <hzpeterchen@...il.com>
CC:	"peter.chen@...escale.com" <peter.chen@...escale.com>,
	"stern@...land.harvard.edu" <stern@...land.harvard.edu>,
	"balbi@...nel.org" <balbi@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"abrestic@...omium.org" <abrestic@...omium.org>,
	"yoshihiro.shimoda.uh@...esas.com" <yoshihiro.shimoda.uh@...esas.com>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface

Hi

> -----Original Message-----
> From: Roger Quadros [mailto:rogerq@...com]
> Sent: Tuesday, May 10, 2016 3:35 PM
> To: Peter Chen <hzpeterchen@...il.com>
> Cc: peter.chen@...escale.com; stern@...land.harvard.edu; balbi@...nel.org;
> 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; yoshihiro.shimoda.uh@...esas.com; linux-
> usb@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> omap@...r.kernel.org; devicetree@...r.kernel.org
> Subject: Re: [PATCH v7 03/14] usb: hcd.h: Add OTG to HCD interface
> 
> On 10/05/16 06:14, Peter Chen wrote:
> > On Mon, May 09, 2016 at 12:45:38PM +0300, Roger Quadros wrote:
> >> On 06/05/16 12:41, Peter Chen wrote:
> >>> On Mon, May 02, 2016 at 03:18:46PM +0300, Roger Quadros wrote:
> >>>> The OTG core will use struct otg_hcd_ops to interface with the HCD
> >>>> controller.
> >>>>
> >>>> The main purpose of this interface is to avoid directly calling HCD
> >>>> APIs from the OTG core as they wouldn't be defined in the built-in
> >>>> symbol table if CONFIG_USB is m.
> >>>>
> >>>> Signed-off-by: Roger Quadros <rogerq@...com>
> >>>> Acked-by: Peter Chen <peter.chen@....com>
> >>>
> >>> Roger, after thinking more, I still think current dependency between
> >>> OTG, HCD and gadget are too complicated. Since the OTG can't work if
> >>> it is built as module, I suggest letting OTG depends on HCD &&
> >>> USB_GADGET, and it is a boolean, in that case, we don't need to
> >>> export any HCD and gadget ops, things will be much simpler.
> >>> What's your opinion?
> >>
> >> How will it work if HCD and USB_GADGET are modules and OTG is built-in?
> >>
> >
> > The OTG will not be compiled at this situation, since it is boolean.
> > In fact, like I mentioned at above, OTG or USB function can't work if
> > it is built as module.
> 
> Isn't this a limitation?
> As per the current implementation dual role works fine even with both
> USB_GADGET and HCD as module.

My understand: only make sense for pass build, host can't work before
gadget modules loaded; gadget can't work before hcd loaded, nothing
can work before all drivers are loaded.

> 
> In the real world it is unlikely that GADGET and HCD will be built-in.

Why? User enable USB_OTG means both drivers should be enabled anyway.
Even in non-OTG case, both may be built-in for machine with 2 ports
(one port is host only, the other one is peripheral only).

A general question, 2 drivers depends on each other, allowable?

> 
> cheers,
> -roger
> 
> >
> > Peter
> >> cheers,
> >> -roger
> >>
> >>>
> >>> Peter
> >>>
> >>>> ---
> >>>>  include/linux/usb/hcd.h | 24 ++++++++++++++++++++++++
> >>>>  1 file changed, 24 insertions(+)
> >>>>
> >>>> diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
> >>>> index b98f831..861ccaa 100644
> >>>> --- a/include/linux/usb/hcd.h
> >>>> +++ b/include/linux/usb/hcd.h
> >>>> @@ -399,6 +399,30 @@ struct hc_driver {
> >>>>
> >>>>  };
> >>>>
> >>>> +/**
> >>>> + * struct otg_hcd_ops - Interface between OTG core and HCD
> >>>> + *
> >>>> + * Provided by the HCD core to allow the OTG core to interface
> >>>> +with the HCD
> >>>> + *
> >>>> + * @add: function to add the HCD
> >>>> + * @remove: function to remove the HCD
> >>>> + * @usb_bus_start_enum: function to immediately start bus
> >>>> +enumeration
> >>>> + * @usb_control_msg: function to build and send of a control urb
> >>>> + * @usb_hub_find_child: function to get pointer to the child
> >>>> +device  */ struct otg_hcd_ops {
> >>>> +	int (*add)(struct usb_hcd *hcd,
> >>>> +		   unsigned int irqnum, unsigned long irqflags);
> >>>> +	void (*remove)(struct usb_hcd *hcd);
> >>>> +	int (*usb_bus_start_enum)(struct usb_bus *bus, unsigned int
> port_num);
> >>>> +	int (*usb_control_msg)(struct usb_device *dev, unsigned int
> pipe,
> >>>> +			       __u8 request, __u8 requesttype, __u16 value,
> >>>> +			       __u16 index, void *data, __u16 size,
> >>>> +			       int timeout);
> >>>> +	struct usb_device * (*usb_hub_find_child)(struct usb_device
> *hdev,
> >>>> +						  int port1);
> >>>> +};
> >>>> +
> >>>>  static inline int hcd_giveback_urb_in_bh(struct usb_hcd *hcd)  {
> >>>>  	return hcd->driver->flags & HCD_BH;
> >>>> --
> >>>> 2.7.4
> >>>>
> >>>> --
> >>>> To unsubscribe from this list: send the line "unsubscribe
> >>>> linux-usb" in the body of a message to majordomo@...r.kernel.org
> >>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> >>>
> >