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

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Date:	Wed, 9 Sep 2015 14:10:57 +0300
From:	Roger Quadros <rogerq@...com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Peter Chen <peter.chen@...escale.com>,
	"Balbi, Felipe" <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Li Jun <jun.li@...escale.com>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Tony Lindgren <tony@...mide.com>, <Joao.Pinto@...opsys.com>,
	Andrew Bresticker <abrestic@...omium.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [PATCH v4 07/13] usb: otg: add OTG core

(adding back folks in cc)

On 08/09/15 20:35, Alan Stern wrote:
> On Tue, 8 Sep 2015, Roger Quadros wrote:
> 
>>>> 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.
>>>
>>> This seems a lot like something Peter and I discussed recently.  See
>>>
>>> 	http://marc.info/?l=linux-usb&m=143977568021328&w=2
>>>
>>> and the following messages in that thread.
>>>
>>
>> If I understood right, your proposal was to add a usb_pointers data
>> struct to the device's drvdata?
> 
> Right.
> 
>> This is fine only if the otg/gadget/host share the same device.
>> It does not solve the problem where each have different platform devices.
> 
> Why not?  Each of the platform devices can store a pointer to the same 
> usb_pointers structure.  Wouldn't that be suitable?
> 

I didn't understand how all of them get the reference to the
same usb_pointer structure (or contents) when their respective platform devices
get created so that they can store it in their respective drvdata.

Worst case, the 3 devices could be totally independent of each other without a
common parent, and get registered at different times.

The common resource here is the physical USB port for which the 3 drivers
otg/host/gadget are being registered.
There should be a mechanism for each device to tell that it is part of
this particular USB port. (or usb_pointers struct)

cheers,
-roger
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