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Date:	Mon, 16 May 2016 11:01:27 +0300
From:	Roger Quadros <rogerq@...com>
To:	Peter Chen <hzpeterchen@...il.com>
CC:	Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	Alan Stern <stern@...land.harvard.edu>,
	Rob Herring <robh@...nel.org>,
	"peter.chen@...escale.com" <peter.chen@...escale.com>,
	"balbi@...nel.org" <balbi@...nel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
	"jun.li@...escale.com" <jun.li@...escale.com>,
	"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
	"tony@...mide.com" <tony@...mide.com>,
	"Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
	"abrestic@...omium.org" <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" <linux-omap@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 10/14] usb: otg: add hcd companion support

On 16/05/16 05:13, Peter Chen wrote:
> On Thu, May 12, 2016 at 03:13:48PM +0300, Roger Quadros wrote:
>> Hi,
>>
>> On 12/05/16 13:31, Yoshihiro Shimoda wrote:
>>> Hi,
>>>
>>>> From: Roger Quadros
>>>> Sent: Thursday, May 12, 2016 6:32 PM
>>>>
>>>> Hi,
>>>>
>>>> On 12/05/16 11:34, Roger Quadros wrote:
>>>>> On 12/05/16 07:00, Yoshihiro Shimoda wrote:
>>>>>> Hi,
>>>>>>
>>>>>>> From: Alan Stern
>>>>>>> Sent: Wednesday, May 11, 2016 11:47 PM
>>>>>>>
>>>>>>> On Wed, 11 May 2016, Roger Quadros wrote:
>>>>>>>
>>>>>>>>> What I mean is if you have 2 EHCI controllers with 2 companion
>>>>>>>>> controllers, don't you need to know which companion goes with which EHCI
>>>>>>>>> controller? Just like you do for the otg-controller property.
>>>>>>>>>
>>>>>>>>
>>>>>>>> That is a very good point. I'm not very sure and it seems that current code won't work
>>>>>>>> with multiple EHCI + companion instances.
>>>>>>
>>>>>> I may misunderstand this topic, but if I use the following environment, it works correctly.
>>>>>>
>>>>>> < My environment >
>>>>>> - an otg controller: Sets hcd-needs-companion.
>>>>>> - ehci0 and ohci0 and a function: They connect to the otg controller using "otg-controller" property.
>>>>>> - ehci1 and ohci1: No "otg-controller" property.
>>>>>> - ehci2 and ohci2: No "otg-controller" property.
>>>>>>
>>>>>> In this environment, all hosts works correctly.
>>>>>> Also I think if we have 2 otg controlelrs, it should be work because otg_dev instance differs.
>>>>>
>>>>> The topic is about more than one otg controllers and how to tie the right ehci and ohci
>>>>> to the correct otg_dev instance especially in cases where we can't depend on probe order.
>>>>>
>>>>>> Or, does this topic assume an otg controller handles 2 EHCI controllers?
>>>>>> I'm not sure such environment actually exists.
>>>>>
>>>>> No it is not about that.
>>>
>>> Thank you for the reply. I understood it.
>>>
>>>>>>>> Alan, does USB core even know which EHCI and OHCI are linked to the same port
>>>>>>>> or the handoff is software transparent?
>>>>>>>
>>>>>>> The core knows.  It doesn't use the information for a whole lot of
>>>>>>> things, but it does use it in a couple of places.  Search for
>>>>>>> "companion" in core/hcd-pci.c and you'll see.
>>>>>>
>>>>>> Thank you for the information. I didn't know this code.
>>>>>> If my understanding is correct, the core/hcd-pci.c code will not be used by non-PCI devices.
>>>>>
>>>>> That is correct.
>>>>>
>>>>>> In other words, nobody sets "hcd->self.hs_companion" if we use such a device.
>>>>>> So, I will try to add such a code if needed.
>>>>>
>>>>> I think OTG core would have to rely on USB core in providing the right companion device,
>>>>> just like we rely on it for the primary vs shared HCD case.
>>>>>
>>>>
>>>> OK, it is not so simple.
>>>>
>>>> EHCI and companion port handoff is really meant to be software transparent.
>>>>
>>>> non-PCI devices really don't have knowledge of which OHCI instance is companion to the EHCI.
>>>> With device tree we could provide this mapping but for non-device tree case we can't do
>>>> anything.
>>>>
>>>> So my suggestion would be to keep dual role implementation limited to one instance for
>>>> EHCI + companion case for non-DT.
>>>> For PCI case I don't see how dual role can be implemented. I don't think we have any
>>>> dual-role PCI cards.
>>>
>>> R-Car Gen2 SoCs (r8a779[0134] / arm32) has USB 2.0 host controllers via PCI bus and
>>> one high speed function controller via AXI bus.
>>> One of channel can be used as host or function.
>>>
>>>> For DT case we could have a DT binding to tie the EHCI and companion and use that
>>>> in the OTG framework.
>>
>> After looking at the code it seems we don't need this special binding as we are already
>> linking the EHCI controller and companion controller to the single otg controller instance
>> using the otg-controller property.
>>
> 
> Then, how you know this EHCI + companion controller special case during otg adds
> hcd, it needs special handling, right?

We know the special case by using the hcd_needs_companion flag.

cheers,
-roger

> 
> Peter
> 
>> So all is good as of now.
>>
>> For non DT case, it is the responsibility of platform support code to ensure that
>> it calls usb_otg_add_hcd() with the correct otg controller instance for both EHCI and
>> companion controller and things should work fine there as well.
>>
>> --
>> cheers,
>> -roger
>>
>>>
>>> R-Car Gen3 SoC (r8a7795 / arm64) will be this type.
>>> (Both USB 2.0 host/function controllers connect to AXI bus.)
>>>
>>>> Any objections?
>>>
>>> I don't have any objections because I'm just focus on R-Car Gen3 SoC for now.
>>> If someone needs for PCI case, I think it is possible to add such a code somehow later.
>>>
>>> Best regards,
>>> Yoshihiro Shimoda
>>>
>>>> cheers,
>>>> -roger
>> --
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> 

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