From: Rajaram R <rajaram.officemail@gmail.com>
To: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Cc: Felipe Balbi <balbi@kernel.org>, Oliver Neukum <oneukum@suse.com>,
Felipe Balbi <balbif@gmail.com>,
Mathias Nyman <mathias.nyman@linux.intel.com>,
Greg KH <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org,
"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: Re: [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface
Date: Thu, 18 Feb 2016 16:07:54 +0530 [thread overview]
Message-ID: <CAOiXhaKYf0XGTNYF=dmwoSZKNGBY+niXHXK9Veo8tSsUpcBeyA@mail.gmail.com> (raw)
In-Reply-To: <20160217142816.GC24649@kuha.fi.intel.com>
On Wed, Feb 17, 2016 at 7:58 PM, Heikki Krogerus
<heikki.krogerus@linux.intel.com> wrote:
> On Wed, Feb 17, 2016 at 03:36:46PM +0200, Felipe Balbi wrote:
>>
>> Hi,
>>
>> Heikki Krogerus <heikki.krogerus@linux.intel.com> writes:
>> > On Wed, Feb 17, 2016 at 11:36:52AM +0100, Oliver Neukum wrote:
>> >> On Wed, 2016-02-17 at 12:29 +0200, Felipe Balbi wrote:
>> >> > Hi,
>> >> >
>> >> > Oliver Neukum <oneukum@suse.com> writes:
>> >> > > On Wed, 2016-02-17 at 09:58 +0200, Heikki Krogerus wrote:
>> >> > >> On Tue, Feb 16, 2016 at 02:39:47PM +0100, Oliver Neukum wrote:
>> >>
>> >> > >> > Yes, but we need an API. We can't keep adding to it. So if that
>> >> > >> > is to be supported, it needs to be defined now.
>> >> > >>
>> >> > >> When you say API, do you mean the API the class provides to the
>> >> > >> drivers? Or did you mean ABI which would be the sysfs in this case?
>> >> > >
>> >> > > The API to user space. That is the point. We cannot break user space.
>> >> > > Once this sysfs API is upstream we are stuck with it.
>> >> >
>> >> > yeah, in fact I have been wondering if sysfs is the best interface to
>> >>
>> >> That is the discussion we must have.
>> >>
>> >> > userspace. I talked with Heikki a few days back about this; I was
>> >> > wondering if something like what the NFC folks did with netlink would be
>> >> > better here.
>> >>
>> >> I doubt that, because the main user is likely to be udev scripts.
>> >> They can easily deal with sysfs attributes.
>> >
>> > IMHO for high level interface like this, sysfs is ideal because of the
>> > simple fact that you only need a shell to access the files. netlink
>> > would make us depend on custom software, no?
>> >
>> > I'm not against using netlink, but what would be the benefit from it
>> > in this case?
>>
>> With HW we see nowadays, CC stack is hidden on some microcontroller, but
>> is it too far-fetched to consider a system where this is not the case ?
>
> There already are several USB PD stacks out there, like also Greg
> pointed out.
>
>> Specially when we consider things like power delivery which, I know, you
>> wanted to keep it out of this interface, however we would have two
>> 'stacks' competing for access to the same pins, right ?
>
> No. This class would be the top layer for the coming stack, where ever
> it ends up coming. The class is only the interface to the user space
> and nothing else.
>
> By saying we need to keep USB Type-C separate from USB PD I meant that
> the userspace access can not be mixed somewhere in layers of the USB
> PD/CC stack like it has been in the USB PD stacks I've seen so far.
> They assume that we always use the software USB PD stack with USB
> Type-C, which as we can see is not true when the stack is implemented
> in EC or firmware or some complex USB PD controller or what ever.
> However, the operations the userspace needs to do are exactly the same
> in both cases.
>
> - data role swapping
> - power role swapping (depends on USB PD)
> - Alternate Modes (depends on USB PD)
>
> And we really should not forget that we actually also have USB Type-C
> PHYs that can't do any USB PD communication over the CC pin, so USB PD
> is simply not always going to be available. But the data role swapping
> and also accessories are still available with them, as the do not need
> USB PD.
>
> This was the whole point with the class. It allows the different ways
> of dealing with Type-C ports to be exposed to userspace in the same
> way.
>
>> IIRC mode and role negotiation goes via CC pins using the power delivery
>> protocol. If I misunderstand anything, let me know.
>
> The data role swap with USB Type-C connectors is in no way tied to USB
> Power Delivery. The USB Type-C spec defines that when USB PD is
Its not data role swap i guess its dual role, A Data role swap is tied
with USB PD,
> available, DR_Swap USB PD function is used to swap the role, otherwise
> emulated disconnect will do the trick.
I doubt a USB host with no device capability implement DRP ?? Also
emulated trick(??) is not spec requirement rt ?
>
> Data role swapping is a must thing to have with USB Type-C connectors
I guess you are referring to Dual role (DRP) and not data role (DRD).
> because of the fact that the role is selected randomly. Regardless was
> USB PD supported or not.
>
>
> Thanks,
>
> --
> heikki
> --
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> More majordomo info at http://vger.kernel.org/majordomo-info.html
next prev parent reply other threads:[~2016-02-18 10:37 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-09 17:01 [PATCH 0/3] usb: USB Type-C Class and driver for UCSI Heikki Krogerus
2016-02-09 17:01 ` [PATCH 1/3] usb: USB Type-C Connector Class Heikki Krogerus
2016-02-09 18:20 ` Greg KH
2016-02-10 10:38 ` Heikki Krogerus
2016-02-10 17:26 ` Greg KH
2016-02-11 14:07 ` Heikki Krogerus
2016-02-10 10:49 ` Oliver Neukum
2016-02-10 11:05 ` Andy Shevchenko
2016-02-10 11:11 ` Heikki Krogerus
2016-02-10 11:14 ` Andy Shevchenko
2016-02-10 11:23 ` Heikki Krogerus
2016-02-15 15:16 ` Oliver Neukum
2016-02-11 8:55 ` Felipe Balbi
2016-02-11 9:08 ` Oliver Neukum
2016-02-11 14:51 ` Heikki Krogerus
2016-02-11 14:36 ` Heikki Krogerus
2016-02-11 14:56 ` Oliver Neukum
2016-02-17 14:07 ` Oliver Neukum
2016-02-18 8:47 ` Heikki Krogerus
2016-02-18 9:21 ` Oliver Neukum
2016-02-18 13:09 ` Heikki Krogerus
2016-02-18 9:35 ` Oliver Neukum
2016-02-18 13:25 ` Heikki Krogerus
2016-02-18 13:44 ` Oliver Neukum
2016-02-18 15:13 ` Heikki Krogerus
2016-02-26 13:09 ` Heikki Krogerus
2016-02-09 17:01 ` [PATCH 2/3] usb: type-c: USB Type-C Connector System Software Interface Heikki Krogerus
2016-02-09 18:21 ` Greg KH
2016-02-10 10:30 ` Heikki Krogerus
2016-02-10 17:20 ` Greg KH
2016-02-11 13:50 ` Heikki Krogerus
2016-02-15 15:30 ` Oliver Neukum
2016-02-16 9:22 ` Heikki Krogerus
2016-02-16 13:39 ` Oliver Neukum
2016-02-17 7:58 ` Heikki Krogerus
2016-02-17 9:03 ` Oliver Neukum
2016-02-17 10:29 ` Felipe Balbi
2016-02-17 10:36 ` Oliver Neukum
2016-02-17 11:11 ` Heikki Krogerus
2016-02-17 13:36 ` Felipe Balbi
2016-02-17 14:28 ` Heikki Krogerus
2016-02-18 9:07 ` Peter Chen
2016-02-18 10:44 ` Heikki Krogerus
2016-02-18 10:37 ` Rajaram R [this message]
2016-02-18 10:47 ` Heikki Krogerus
2016-02-18 11:06 ` Rajaram R
2016-02-17 13:34 ` Felipe Balbi
2016-02-17 13:51 ` Oliver Neukum
2016-02-18 7:08 ` Felipe Balbi
2016-02-18 10:18 ` Oliver Neukum
2016-02-18 10:30 ` Felipe Balbi
2016-02-18 10:40 ` Oliver Neukum
2016-02-18 9:29 ` Peter Chen
2016-02-18 9:44 ` Oliver Neukum
2016-02-10 11:19 ` Oliver Neukum
2016-02-10 12:04 ` Heikki Krogerus
2016-02-10 11:56 ` Andy Shevchenko
2016-02-10 13:21 ` Oliver Neukum
2016-02-10 14:02 ` Andy Shevchenko
2016-02-10 15:11 ` Bjørn Mork
2016-02-11 8:26 ` Andy Shevchenko
2016-02-11 8:59 ` Bjørn Mork
2016-02-10 14:15 ` Oliver Neukum
2016-02-10 14:24 ` Andy Shevchenko
2016-02-10 15:08 ` Oliver Neukum
[not found] ` <CAHp75VfmGsskf7Cmni3b4=tCbkPsR8d3jPYiv93Lm6DM9gq1-g@mail.gmail.com>
2016-02-11 8:13 ` Fwd: " Andy Shevchenko
2016-02-11 14:10 ` Heikki Krogerus
2016-02-10 13:04 ` Oliver Neukum
2016-02-11 14:08 ` Heikki Krogerus
2016-02-09 17:01 ` [PATCH 3/3] usb: type-c: UCSI ACPI driver Heikki Krogerus
2016-02-09 18:22 ` Greg KH
2016-02-10 10:23 ` Heikki Krogerus
2016-02-17 18:53 ` [PATCH 0/3] usb: USB Type-C Class and driver for UCSI Oliver Neukum
2016-02-18 9:21 ` Heikki Krogerus
2016-02-17 19:34 ` Rajaram R
2016-02-18 11:05 ` Heikki Krogerus
2016-02-18 11:15 ` Oliver Neukum
2016-05-05 3:05 ` Guenter Roeck
2016-05-06 6:50 ` Felipe Balbi
2016-05-06 8:05 ` Guenter Roeck
2016-05-06 8:29 ` Heikki Krogerus
2016-05-06 14:10 ` Guenter Roeck
2016-05-06 8:23 ` Heikki Krogerus
2016-05-06 8:08 ` Heikki Krogerus
2016-05-06 14:08 ` Guenter Roeck
2016-05-11 3:14 ` Guenter Roeck
2016-05-11 9:40 ` Heikki Krogerus
2016-05-11 14:47 ` Guenter Roeck
2016-05-13 14:23 ` Heikki Krogerus
2016-05-13 17:48 ` Guenter Roeck
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