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

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Date:	Tue, 8 Sep 2015 15:25:25 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <peter.chen@...escale.com>
CC:	<stern@...land.harvard.edu>, <balbi@...com>,
	<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>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH v4 07/13] usb: otg: add OTG core



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.

> 
> 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()

cheers,
-roger
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