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

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Date:	Tue, 10 May 2016 11:12:32 +0300
From:	Felipe Balbi <balbi@...nel.org>
To:	Roger Quadros <rogerq@...com>, Peter Chen <hzpeterchen@...il.com>
Cc:	peter.chen@...escale.com, stern@...land.harvard.edu,
	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


Hi,

Roger Quadros <rogerq@...com> writes:
> 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?

I agree, it should work built-in or module.

> 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.

we can't make this assumption, however :-)

-- 
balbi

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