Hi,

Peter Chen [off-list ref] writes:

quoted

quoted

quoted

quoted

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.

quoted

quoted

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.

quoted

quoted

quoted

quoted

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