From: Felipe Balbi <balbi@kernel.org>
To: Peter Chen <hzpeterchen@gmail.com>
Cc: Roger Quadros <rogerq@ti.com>,
peter.chen@freescale.com, tony@atomide.com,
gregkh@linuxfoundation.org, dan.j.williams@intel.com,
mathias.nyman@linux.intel.com, Joao.Pinto@synopsys.com,
sergei.shtylyov@cogentembedded.com, jun.li@freescale.com,
grygorii.strashko@ti.com, yoshihiro.shimoda.uh@renesas.com,
robh@kernel.org, nsekhar@ti.com, b-liu@ti.com, joe@perches.com,
linux-usb@vger.kernel.org, linux-omap@vger.kernel.org,
linux-kernel@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v11 08/14] usb: otg: add OTG/dual-role core
Date: Tue, 21 Jun 2016 10:26:00 +0300 [thread overview]
Message-ID: <877fdjovef.fsf@linux.intel.com> (raw)
In-Reply-To: <20160621060517.GA5108@shlinux2>
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Hi,
Peter Chen <hzpeterchen@gmail.com> writes:
>> >> > It provides APIs for the following tasks
>> >> >
>> >> > - Registering an OTG/dual-role capable controller
>> >> > - Registering Host and Gadget controllers to OTG core
>> >> > - Providing inputs to and kicking the OTG state machine
>> >>
>> >> I think I have already mentioned this, but after over 10 years of OTG,
>> >> nobody seems to care about it, why are we still touching at all I don't
>> >> know. For common non-OTG role-swapping we really don't need any of this
>> >> and, quite frankly, I fail to see enough users for this.
>> >>
>> >> Apparently there's only chipidea which, AFAICT, already had working
>> >> dual-role before this OTG State Machine was added to the kernel.
>> >
>> > Some users would like to know if vendor's platform is OTG compliance,
>> > so we add it to pass usb.org USB OTG certification test.
>>
>> I strongly doubt that's really what they mean. IMHO, users want to know
>> if they can swap roles. Ask them if they are really going for OTG
>> certification. Ask them if they have an OPT tester. Ask them if they
>> really want all those timers. If they want HNP polling, etc etc etc.
>>
>> So far, I haven't seen anybody talking about real USB OTG (the spec)
>> when they say OTG. Usually they just mean "a method for swapping between
>> host and peripheral roles, but we really don't want all the extra cost
>> of the OTG specification".
>>
>
> That's what I thought before, but the request from the Marketing guy is
> "To prove the SoC is OTG compliance, support HNP and SRP", don't you
> see the SoC reference manual say "it supports HNP and SRP"?
>
> If there is no request, who else wants to implement so complicated FSM
> but seldom use cases, and go to pass OTG compliance test (tested by PET).
I stand corrected :-)
So there is one user for this layer. And this user has its own role
control registers. I'm not convinced we need this large generic layer
for one user.
>> > For the real use case, some Carplay platforms need it.
>>
>> Carplay does *NOT* rely on OTG. Apple has its own proprietary and closed
>> specification which is not OTG-compliant.
>>
>
> Yes, it is not OTG-compliant, but it can co-work with some standard OTG FSM
> states to finish role swap.
What are you referring to as "finish role swap"? I don't get that.
> Notice, it needs to swap role without disconnect cable.
right, I can swap role without changing cable, but that's not OTG. The
mechanism for that, AFAICT, is not HNP. I don't know details about
CarPlay because the spec isn't public, but my understanding is that
CarPlay doesn't rely on anything from OTG spec.
>> >> > diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
>> >> > index f4fc0aa..1d74fb8 100644
>> >> > --- a/include/linux/usb/gadget.h
>> >> > +++ b/include/linux/usb/gadget.h
>> >> > @@ -328,6 +328,7 @@ struct usb_gadget_ops {
>> >> > * @in_epnum: last used in ep number
>> >> > * @mA: last set mA value
>> >> > * @otg_caps: OTG capabilities of this gadget.
>> >> > + * @otg_dev: OTG controller device, if needs to be used with OTG core.
>> >>
>> >> do you really know of any platform which has a separate OTG controller?
>> >>
>> >
>> > It may not be a real separate OTG controller. It can be a hardware part
>> > (external connector, external IC, SoC OTG register area, etc) to handle vbus
>> > ,id and other signals which are used for role swap.
>>
>> That's already solved. EXTCON solved that years back and OMAP has been
>> using EXTCON to program its UTMI mailbox.
>>
>
> No, that's not the same thing, it does not include the swap role.
Read your original comment:
"handle vbus, id and other signals which are *used for* role swap"
You didn't include role swap in your original comment. Semantics aside...
> Consider the use case the host driver is at host/ and udc driver is
> at gadget/udc, how to finish to role swap?
... why does the source code placement matter? And what do you mean by
"finish role swap"?
--
balbi
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next prev parent reply other threads:[~2016-06-21 7:27 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-10 13:07 [PATCH v10 00/14] USB OTG/dual-role framework Roger Quadros
2016-06-10 13:07 ` [PATCH v10 01/14] usb: hcd: Initialize hcd->flags to 0 Roger Quadros
2016-06-14 8:16 ` Roger Quadros
2016-06-10 13:07 ` [PATCH v10 02/14] usb: otg-fsm: Prevent build warning "VDBG" redefined Roger Quadros
2016-06-10 13:07 ` [PATCH v10 03/14] usb: hcd.h: Add OTG to HCD interface Roger Quadros
2016-06-14 8:17 ` Roger Quadros
2016-06-14 14:21 ` Alan Stern
2016-06-15 7:14 ` Roger Quadros
2016-06-10 13:07 ` [PATCH v10 04/14] usb: otg-fsm: use usb_otg wherever possible Roger Quadros
2016-06-10 13:07 ` [PATCH v10 05/14] usb: otg-fsm: move host controller operations into usb_otg->hcd_ops Roger Quadros
2016-06-10 13:07 ` [PATCH v10 06/14] usb: gadget.h: Add OTG to gadget interface Roger Quadros
2016-06-12 9:13 ` Peter Chen
2016-06-20 7:21 ` Felipe Balbi
2016-06-20 7:28 ` Roger Quadros
2016-06-20 8:13 ` Felipe Balbi
2016-06-20 8:25 ` Roger Quadros
2016-06-20 9:24 ` Felipe Balbi
2016-06-20 9:43 ` Roger Quadros
2016-06-10 13:07 ` [PATCH v10 07/14] usb: otg: get rid of CONFIG_USB_OTG_FSM in favour of CONFIG_USB_OTG Roger Quadros
2016-06-10 13:07 ` [PATCH v10 08/14] usb: otg: add OTG/dual-role core Roger Quadros
2016-06-12 11:21 ` Peter Chen
2016-06-13 7:42 ` Roger Quadros
2016-06-13 7:56 ` [PATCH v11 " Roger Quadros
2016-06-13 7:58 ` Peter Chen
2016-06-20 7:45 ` Felipe Balbi
2016-06-20 10:13 ` Roger Quadros
2016-06-20 12:03 ` Felipe Balbi
2016-06-20 12:26 ` Roger Quadros
2016-06-20 12:46 ` Felipe Balbi
2016-06-21 6:39 ` Peter Chen
2016-06-21 7:19 ` Felipe Balbi
2016-06-21 8:02 ` Peter Chen
2016-06-21 8:18 ` Felipe Balbi
2016-06-21 9:14 ` Peter Chen
2016-06-21 12:35 ` Felipe Balbi
2016-06-21 13:12 ` Peter Chen
2016-06-21 14:47 ` Felipe Balbi
2016-06-22 3:33 ` Peter Chen
2016-06-22 6:51 ` Felipe Balbi
2016-06-22 7:30 ` Peter Chen
2016-06-22 8:00 ` Felipe Balbi
2016-06-23 7:41 ` Yoshihiro Shimoda
2016-06-21 2:30 ` Yoshihiro Shimoda
2016-06-21 7:21 ` Felipe Balbi
2016-06-20 11:49 ` Peter Chen
2016-06-20 12:08 ` Felipe Balbi
2016-06-21 6:05 ` Peter Chen
2016-06-21 7:26 ` Felipe Balbi [this message]
2016-06-21 9:07 ` Peter Chen
2016-06-21 10:02 ` Felipe Balbi
2016-06-21 10:43 ` Tony Lindgren
2016-06-21 10:56 ` Felipe Balbi
2016-06-21 13:05 ` Peter Chen
2016-06-22 6:56 ` Felipe Balbi
2016-06-22 7:33 ` Peter Chen
2016-06-22 8:03 ` Felipe Balbi
2016-06-22 7:49 ` Roger Quadros
2016-06-22 8:14 ` Felipe Balbi
2016-06-22 8:30 ` Roger Quadros
2017-01-19 11:56 ` Vivek Gautam
2017-01-19 12:15 ` Roger Quadros
2017-01-19 15:15 ` vivek.gautam
2017-01-20 8:30 ` Roger Quadros
2017-01-20 11:39 ` Vivek Gautam
2016-06-23 7:42 ` Yoshihiro Shimoda
2016-06-10 13:07 ` [PATCH v10 09/14] usb: of: add an API to get OTG device from USB controller node Roger Quadros
2016-06-13 8:13 ` Jun Li
2016-06-13 8:16 ` Roger Quadros
2016-06-13 8:23 ` [PATCH v11 " Roger Quadros
2016-06-10 13:07 ` [PATCH v10 10/14] usb: otg: add hcd companion support Roger Quadros
2016-06-10 13:07 ` [PATCH v10 11/14] usb: otg: use dev_vdbg() instead of VDBG() Roger Quadros
2016-06-10 13:07 ` [PATCH v10 12/14] usb: hcd: Adapt to OTG core Roger Quadros
2016-06-14 8:17 ` Roger Quadros
2016-06-10 13:07 ` [PATCH v10 13/14] usb: gadget: udc: adapt " Roger Quadros
2016-06-12 11:36 ` Peter Chen
2016-06-13 7:14 ` Roger Quadros
2016-06-13 7:20 ` Peter Chen
2016-06-13 7:37 ` Roger Quadros
2016-06-13 7:40 ` Peter Chen
2016-06-13 7:55 ` [PATCH v11 " Roger Quadros
2016-06-13 7:56 ` Peter Chen
2016-06-13 8:06 ` Roger Quadros
2016-06-10 13:07 ` [PATCH v10 14/14] usb: host: xhci-plat: Add otg device to platform data Roger Quadros
2016-06-14 8:18 ` Roger Quadros
2016-06-14 2:17 ` [PATCH v10 00/14] USB OTG/dual-role framework Peter Chen
2016-06-14 8:12 ` Roger Quadros
2016-06-16 11:07 ` Roger Quadros
2016-06-17 7:17 ` Felipe Balbi
2016-06-17 7:31 ` Roger Quadros
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