Date:	Mon, 23 May 2016 13:11:48 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	Jun Li <jun.li@....com>,
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Subject: Re: [PATCH v8 13/14] usb: gadget: udc: adapt to OTG core

On 23/05/16 06:21, Peter Chen wrote:
> On Sat, May 21, 2016 at 10:29:40AM +0800, Peter Chen wrote:
>> On Thu, May 19, 2016 at 10:32:44AM +0300, Roger Quadros wrote:
>>> On 18/05/16 17:46, Jun Li wrote:
>>>>
>>>>
>>>>>>>
>>>>>>> I didn't want to have complex Kconfig so decided to have otg as
>>>>>>> built-in only.
>>>>>>> What do you want me to change in existing code? and why?
>>>>>>
>>>>>> Remove those stuff which only for pass diff driver config Like every
>>>>>> controller driver need a duplicated
>>>>>>
>>>>>> static struct otg_hcd_ops ci_hcd_ops = {
>>>>>>     ...
>>>>>> }
>>>>>
>>>>> This is an exception only. Every controller driver doesn't need to
>>>>> implement hcd_ops. It is implemented in the hcd core.
>>>>>
>>>>>>
>>>>>> And here is another example, for gadget connect, otg driver can
>>>>>> directly call to usb_udc_vbus_handler() in drd state machine, but you
>>>>>> create another interface:
>>>>>>
>>>>>> .connect_control = usb_gadget_connect_control,
>>>>>>
>>>>>> If the symbol is defined in one driver which is 'm', another driver
>>>>>> reference it should be 'm' as well, then there is no this kind of
>>>>>> problem as my understanding.
>>>>>
>>>>> That is fine as long as all are 'm'. but how do you solve the case when
>>>>> Gadget is built in and host is 'm'? OTG has to be built-in and you will
>>>>> need an hcd to gadget interface.
>>>>
>>>> Hcd to gadget interface? Or you want to say otg to host interface?
>>>
>>> Sorry, I meant to say host to otg interface.
>>>
>>>>
>>>> I think hcd and gadget are independent each other, now
>>>>
>>>> Hcd --> otg; and gadget --> otg, (hcd and gadget use otg's symbol)
>>>
>>> It is actually a circular dependency for both.
>>>  hcd <--> otg and gadget <--> otg
>>>
>>> hcd -> otg for usb_otg_register/unregister_hcd
>>> otg -> hcd for usb_add/remove_hcd, usb_bus_start_enum, usb_control_msg, usb_hub_find_child
>>>
>>> gadget -> otg for usb_otg_register/unregister_gadget
>>> otg -> gadget for usb_gadget_start/stop, usb_udc_vbus_handler
>>>
>>> Now consider what will happen if I get rid of the otg_hcd and otg_gadget interfaces.
>>> 'y' means built-in, 'm' means module.
>>>
>>> 1) hcd 'y', gadget 'y'
>>> otg has to be 'y' for proper build.
>>>
>>> 2) hcd 'm', gadget 'm'
>>> otg has to be 'm' for proper build.
>>>
>>> 3) hcd 'y', gadget 'm'
>>> Build will fail always.
>>> If otg is 'y', otg build will fail due to dependency on gadget.
>>> If otg is 'm', hcd build will fail due to dependency on otg.
>>>
>>> 4) hcd 'm', gadget 'y'
>>> Build will fail always.
>>> If otg is 'y', otg build will fail due to dependency on hcd.
>>> If otg is 'm', gadget build will fails due to dependency on otg.
>>>
>>> So I solve this problem by adding the otg_hcd_ops and otg_gadget_ops
>>> to remove otg->hcd and otg->gadget dependency.
>>>
>>> Now we can address 3) and 4) like so
>>>
>>> 3) hcd 'y', gadget 'm'
>>> otg has to be 'y' for proper build.
>>>
>>> 4) hcd 'm', gadget 'y'
>>> otg has to be 'y' for proper build.
>>>
>>
>> How about this:
>> Moving usb_otg_register/unregister_hcd to host driver to remove
>> dependency hcd->otg. And moving usb_otg_get_data to common.c.
>>
>> Delete the wait queue at usb-otg.c, and if calling usb_otg_get_data
>> returns NULL, the host/device driver's probe return -EPROBE_DEFER.
>> When the otg driver is probed successfully, the host/device will be
>> re-probed again, and usb_otg_register_hcd will be called again.
>>
>> And let OTG depends on HCD && GADGET, and delete otg_hcd_ops and
>> otg_gadget_ops. Below build dependency issues can be fixed.
>> What do you think?
>>
>>> 1) hcd 'y', gadget 'y'
>>> otg has to be 'y' for proper build.
>>>
>>> 2) hcd 'm', gadget 'm'
>>> otg has to be 'm' for proper build.
>>>
>>> 3) hcd 'y', gadget 'm'
>>> Build will fail always.
>>> If otg is 'y', otg build will fail due to dependency on gadget.
>>> If otg is 'm', hcd build will fail due to dependency on otg.
>>>
>>> 4) hcd 'm', gadget 'y'
>>> Build will fail always.
>>> If otg is 'y', otg build will fail due to dependency on hcd.
>>> If otg is 'm', gadget build will fails due to dependency on otg.
>> -- 
>>
> 
> After thinking more, my suggestion can't work. How about moving
> CONFIG_USB_OTG out of CONFIG_USB, in that case, CONFIG_USB_OTG
> can only be built in.
> 
I tried this but it still doesn't resolve 3 and 4. I.e.
it can't be automatically set to 'y' when either of hcd/gadget is 'y'
and the other is 'm'.

I think some kconfig trickery can be done to get what we want.

cheers,
-roger

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