Re: [PATCH v4 07/13] usb: otg: add OTG core

[Roger Quadros]

On 09/09/15 05:21, Peter Chen wrote:
> On Tue, Sep 08, 2015 at 03:25:25PM +0300, Roger Quadros wrote:
>>
>>
>> On 08/09/15 11:31, Peter Chen wrote:
>>> On Mon, Sep 07, 2015 at 01:23:01PM +0300, Roger Quadros wrote:
>>>> On 07/09/15 04:23, Peter Chen wrote:
>>>>> On Mon, Aug 24, 2015 at 04:21:18PM +0300, Roger Quadros wrote:
>>>>>> + * This is used by the USB Host stack to register the Host controller
>>>>>> + * to the OTG core. Host controller must not be started by the
>>>>>> + * caller as it is left upto the OTG state machine to do so.
>>>>>> + *
>>>>>> + * Returns: 0 on success, error value otherwise.
>>>>>> + */
>>>>>> +int usb_otg_register_hcd(struct usb_hcd *hcd, unsigned int irqnum,
>>>>>> +			 unsigned long irqflags, struct otg_hcd_ops *ops)
>>>>>> +{
>>>>>> +	struct usb_otg *otgd;
>>>>>> +	struct device *hcd_dev = hcd->self.controller;
>>>>>> +	struct device *otg_dev = usb_otg_get_device(hcd_dev);
>>>>>> +
>>>>>
>>>>> One big problem here is: there are two designs for current (IP) driver
>>>>> code, one creates dedicated hcd device as roothub's parent, like dwc3.
>>>>> Another one doesn't do this, roothub's parent is core device (or otg device
>>>>> in your patch), like chipidea and dwc2.
>>>>>
>>>>> Then, otg_dev will be glue layer device for chipidea after that.
>>>>
>>>> OK. Let's add a way for the otg controller driver to provide the host and gadget
>>>> information to the otg core for such devices like chipidea and dwc2.
>>>>
>>>
>>> Roger, not only chipidea and dwc2, I think the musb uses the same
>>> hierarchy. If the host, device, and otg share the same register
>>> region, host part can't be a platform driver since we don't want
>>> to remap the same register region again.
>>>
>>> So, in the design, we may need to consider both situations, one
>>> is otg/host/device has its own register region, and host is a
>>> separate platform device (A), the other is three parts share the
>>> same register region, there is only one platform driver (B).
>>>
>>> A:
>>>
>>> 			IP core device 
>>> 			    |
>>> 			    |
>>> 		      |-----|-----|
>>> 		      gadget   host platform device	
>>> 		      		|
>>> 				roothub
>>>
>>> B:
>>>
>>> 			IP core device
>>> 			    |
>>> 			    |
>>> 		      |-----|-----|
>>> 		      gadget   	 roothub
>>> 		      		
>>>
>>>> This API must be called before the hcd/gadget-driver is added so that the otg
>>>> core knows it's linked to an OTG controller.
>>>>
>>>> Any better idea?
>>>>
>>>
>>> A flag stands for this hcd controller is the same with otg controller
>>> can be used, this flag can be stored at struct usb_otg_config.
>>
>> What if there is another architecture like so?
>>
>> C:
>> 			[Parent]
>> 			   |
>> 			   |
>> 		|------------------|--------------|
>> 	[OTG core]		[gadget]	[host]
>>
>> We need a more flexible mechanism to link the gadget and
>> host device to the otg core for non DT case.
>>
>> How about adding struct usb_otg parameter to usb_otg_register_hcd()?
>>
>> e.g.
>> int usb_otg_register_hcd(struct usb_otg *otg, struct usb_hcd *hcd, ..)
>>
>> If otg is NULL it will try DT otg-controller property or parent to
>> get the otg controller.
> 
> How usb_otg_register_hcd get struct usb_otg, from where?

This only works when the parent driver creating the hcd has registered the
otg controller too.

> 
>>
>>>
>>> Peter
>>>
>>> P.S: I still read your code, I find not all APIs in this file are used
>>> in your dwc3 example. 
>>
>> Which ones? The ones for registering/unregistered host/gadget are used
>> by hcd/udc core as part of usb_add/remove_hcd() and
>> udc_bind_to_driver()/usb_gadget_remove_driver()
>>
> 
> Ok, now I understand your design, usb_create_hcd must be called before
> the fsm kicks off. The call flow like below:
> 
> usb_otg_register->usb_create_hcd->usb_add_hcd->usb_otg_register_hcd->
> usb_otg_start_host->usb_otg_add_hcd

Actually these are the discrete steps
- usb_otg_register
- usb_create_hcd
- usb_add_hcd->usb_otg_register_hcd  (HCD is not really added till FSM in host role)

Above 3 are prerequisite for FSM to start in addition to gadget controller and
driver being ready.

When FSM enters in host role
- usb_otg_start_host(true)->usb_otg_add_hcd (Now HCD is added)

When FSM exits host role
- usb_otg_start_host(false)->usb_otg_remove_hcd (Now HCD is removed, but not unregistered)

If HCD hardware really goes away
- usb_remove_hcd->usb_otg_unregister_hcd (Now FSM stops as host resource not available)

> 
> We need to make some changes to let chipidea work since usb_create_hcd
> is included at host->start.
> 

Yes, you just need to do the usb_add_hcd() in probe
and usb_otg_start_host() during role switch.

cheers,
-roger
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/