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

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Message-ID: <57318F19.7000506@ti.com>
Date:	Tue, 10 May 2016 10:34:49 +0300
From:	Roger Quadros <rogerq@...com>
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.

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

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
>>>>
>>>> --
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>>>
>