linux-kernel - Re: [PATCH v10 06/14] usb: gadget.h: Add OTG to gadget interface

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Date:	Mon, 20 Jun 2016 12:24:53 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Roger Quadros <rogerq@...com>, peter.chen@...escale.com
Cc:	tony@...mide.com, gregkh@...uxfoundation.org,
	dan.j.williams@...el.com, mathias.nyman@...ux.intel.com,
	Joao.Pinto@...opsys.com, sergei.shtylyov@...entembedded.com,
	jun.li@...escale.com, grygorii.strashko@...com,
	yoshihiro.shimoda.uh@...esas.com, robh@...nel.org, nsekhar@...com,
	b-liu@...com, joe@...ches.com, linux-usb@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org
Subject: Re: [PATCH v10 06/14] usb: gadget.h: Add OTG to gadget interface


Hi,

Roger Quadros <rogerq@...com> writes:
>>>> Roger Quadros <rogerq@...com> writes:
>>>>> The OTG core will use struct otg_gadget_ops to
>>>>> start/stop the gadget controller.
>>>>>
>>>>> The main purpose of this interface is to avoid directly
>>>>> calling usb_gadget_start/stop() from the OTG core as they
>>>>> wouldn't be defined in the built-in symbol table if
>>>>> CONFIG_USB_GADGET is m.
>>>>>
>>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>>> ---
>>>>>  include/linux/usb/gadget.h | 16 ++++++++++++++++
>>>>>  1 file changed, 16 insertions(+)
>>>>>
>>>>> diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
>>>>> index 2dd9e6b..f4fc0aa 100644
>>>>> --- a/include/linux/usb/gadget.h
>>>>> +++ b/include/linux/usb/gadget.h
>>>>> @@ -639,6 +639,22 @@ struct usb_gadget_driver {
>>>>>  };
>>>>>  
>>>>>  
>>>>> +/*-------------------------------------------------------------------------*/
>>>>> +
>>>>> +/**
>>>>> + * struct otg_gadget_ops - Interface between OTG core and gadget
>>>>> + *
>>>>> + * Provided by the gadget core to allow the OTG core to start/stop the gadget
>>>>> + *
>>>>> + * @start: function to start the gadget
>>>>> + * @stop: function to stop the gadget
>>>>> + * @connect_control: function to connect/disconnect from the bus
>>>>> + */
>>>>> +struct otg_gadget_ops {
>>>>> +	int (*start)(struct usb_gadget *gadget);
>>>>> +	int (*stop)(struct usb_gadget *gadget);
>>>>> +	int (*connect_control)(struct usb_gadget *gadget, bool connect);
>>>>> +};
>>>>
>>>> you shouldn't need these at all. They are already part of the gadget
>>>> framework as ->udc_start(), ->udc_stop() and ->pullup()
>>>>
>>>
>>> This is to avoid the undefined symbol errors during build when OTG has is
>>> built-in because USB (host) is built-in but GADGET is still a module.
>> 
>> change your Kconfig dependencies. OTG layer shouldn't be built-in unless
>> both Gadget and Host are built-in.
>> 
>
> That is only one side of the story.
> What happens if OTG is (m), Host is (m) but Gadget is (built in).
>
> Gadget build will fail because of undefined symbol errors for all of
> the OTG APIs.

So you created a circular dependency, right? That's not good either. I
suggest you clean that up because this is bound to create randconfig
build problems in the long run.

-- 
balbi

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