Re: [PATCH v8 13/14] usb: gadget: udc: adapt to OTG core

[Roger Quadros]

On 23/05/16 13:34, Jun Li wrote:
> Hi
> 
>> -----Original Message-----
>> From: Roger Quadros [mailto:rogerq@xxxxxx]
>> Sent: Monday, May 23, 2016 6:12 PM
>> To: Peter Chen <hzpeterchen@xxxxxxxxx>
>> Cc: Jun Li <jun.li@xxxxxxx>; peter.chen@xxxxxxxxxxxxx; balbi@xxxxxxxxxx;
>> tony@xxxxxxxxxxx; gregkh@xxxxxxxxxxxxxxxxxxx; dan.j.williams@xxxxxxxxx;
>> mathias.nyman@xxxxxxxxxxxxxxx; Joao.Pinto@xxxxxxxxxxxx;
>> sergei.shtylyov@xxxxxxxxxxxxxxxxxx; jun.li@xxxxxxxxxxxxx;
>> grygorii.strashko@xxxxxx; yoshihiro.shimoda.uh@xxxxxxxxxxx;
>> robh@xxxxxxxxxx; nsekhar@xxxxxx; b-liu@xxxxxx; linux-usb@xxxxxxxxxxxxxxx;
>> linux-omap@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
>> devicetree@xxxxxxxxxxxxxxx
>> 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'.
> 
> USB_OTG only can be selected by *user*, can't be automatically set to
> 'y' like you said, no matter what's hcd/gadget config, USB_OTG can be
> disabled in any cases.

Yes. I am on the same page with that.
> 
> I think Peter's intention is to make USB_OTG to be 'bool', either disabled;
> or built-in(if enabled), something like your original idea?

I'm fine with my original idea if you guys can confirm :).

cheers,
-roger
> 
> Li Jun
> 
>>
>> I think some kconfig trickery can be done to get what we want.
>>
>> cheers,
>> -roger