linux-kernel - Re: [PATCH v7 10/14] usb: otg: add hcd companion support

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Date:	Wed, 11 May 2016 17:13:19 +0300
From:	Roger Quadros <rogerq@...com>
To:	Rob Herring <robh@...nel.org>, <stern@...land.harvard.edu>,
	<yoshihiro.shimoda.uh@...esas.com>
CC:	<peter.chen@...escale.com>, <balbi@...nel.org>,
	<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>,
	<devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 10/14] usb: otg: add hcd companion support



On 11/05/16 16:54, Rob Herring wrote:
> On Wed, May 04, 2016 at 04:47:18PM +0300, Roger Quadros wrote:
>> On 04/05/16 16:17, Rob Herring wrote:
>>> On Mon, May 02, 2016 at 03:18:53PM +0300, Roger Quadros wrote:
>>>> From: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>>>
>>>> Since some host controller (e.g. EHCI) needs a companion host controller
>>>> (e.g. OHCI), this patch adds such a configuration to use it in the OTG
>>>> core.
>>>>
>>>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>>> Signed-off-by: Roger Quadros <rogerq@...com>
>>>> ---
>>>>  Documentation/devicetree/bindings/usb/generic.txt |  3 +++
>>>>  drivers/usb/common/usb-otg.c                      | 32 ++++++++++++++++-------
>>>>  include/linux/usb/otg.h                           |  7 ++++-
>>>>  3 files changed, 32 insertions(+), 10 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/usb/generic.txt b/Documentation/devicetree/bindings/usb/generic.txt
>>>> index f6866c1..1db1c33 100644
>>>> --- a/Documentation/devicetree/bindings/usb/generic.txt
>>>> +++ b/Documentation/devicetree/bindings/usb/generic.txt
>>>> @@ -27,6 +27,9 @@ Optional properties:
>>>>   - otg-controller: phandle to otg controller. Host or gadget controllers can
>>>>  			contain this property to link it to a particular OTG
>>>>  			controller.
>>>> + - hcd-needs-companion: must be present if otg controller is dealing with
>>>> +			EHCI host controller that needs a companion OHCI host
>>>> +			controller.
>>>
>>> Don't you need to have a link to the companion controller node?
>>
>> primary and companion controllers are totally independent of each other
>> e.g. EHCI and OHCI. They are enabled by separate Kconfig options and
>> the system can operate with either or both of them enabled.
>>
>> At the OTG layer we don't have information as to whether we should be waiting
>> for both of them to register or not and hence need this "hcd-needs-companion" flag.
> 
> 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.

Alan, does USB core even know which EHCI and OHCI are linked to the same port
or the handoff is software transparent?

cheers,
-roger