From: Robert Baldyga <r.baldyga@samsung.com>
To: Roger Quadros <rogerq@ti.com>, Chanwoo Choi <cw00.choi@samsung.com>
Cc: myungjoo.ham@samsung.com, linux-usb@vger.kernel.org,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
m.szyprowski@samsung.com
Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection
Date: Thu, 09 Apr 2015 12:18:27 +0200 [thread overview]
Message-ID: <552651F3.209@samsung.com> (raw)
In-Reply-To: <55264D8B.7010301@ti.com>
On 04/09/2015 11:59 AM, Roger Quadros wrote:
> Hi,
>
> On 09/04/15 12:24, Robert Baldyga wrote:
>> Hi Chanwoo,
>>
>> On 04/09/2015 11:07 AM, Chanwoo Choi wrote:
>>> Hi Robert,
>>>
>>> On 04/09/2015 04:57 PM, Robert Baldyga wrote:
>>>> Hi Chanwoo,
>>>>
>>>> On 04/09/2015 04:12 AM, Chanwoo Choi wrote:
>>>>> Hi Robert,
>>>>>
>>>
>>> [snip]
>>>
>>>>> But, I have one question about case[3]
>>>>>
>>>>> If id is low and vbus is high, this patch will update the state of both USB and USB-HOST cable as attached state.
>>>>> Is it possible that two different cables (both USB and USB-HOST) are connected to one port simultaneously?
>>>>>
>>>>
>>>> It's because state of single USB cable connection cannot be completely
>>>> described using single extcon cable. USB cable state has two bits (VBUS
>>>> and ID), so we need to use two cables for single cable connection. We
>>>> use following convention:
>>>> cable "USB" = VBUS
>>>> cable "USB-HOST" = !ID.
>>>
>>> I think that extcon provider driver have to update the only one cable state
>>> of either USB or USB-HOST because USB and USB-HOST feature can not be used
>>> at the same time through one h/w port.
>
> At least for the kernel users [1] we are treating USB-HOST as !ID and USB as VBUS.
> So it is not an issue for these kernel users if both USB and USB-HOST are attached.
> This is a valid USB state.
> If we don't do so then extcon with 3 cable states is not sufficient to capture the
> entire USB scenario. (we need 4 states for 2 pins).
>
> [1]
> - drivers/usb/phy/phy-omap-otg.c
> - drivers/usb/dwc3/dwc3-omap.c
>
>
>>>
>>> If extcon-usb-gpio.c update two connected event of both USB and USB-HOST cable
>>> at the same time, the extcon consumer driver can not decide what handle either USB or USB-HOST.
>>>
>>
>> It can. USB OTG allows for that. Moreover device can be host even if
>> ID=1 (so detected cable type is USB device), or peripheral when ID=0 (so
>> detected cable type is USB host). Devices would need to have complete
>> information about USB cable connection, because OTG state machine needs
>> that. As I wrote, current USB cable names are misleading. It would be
>> better to have "USB-VBUS" and "USB-ID".
>
> We need to first understand how user space is using "USB" and "USB-HOST" events
> and does it cause an issue if both USB and USB-HOST become attached.
>
> What is the "ABI" explanation for "USB" and "USB-HOST" cable states?
>
We can also leave USB and USB-HOST as "dummy cable detection states",
like they currently are, and add new USB-VBUS and USB-ID cables without
removing the old ones. It will cause some redundancy, but will make us
sure, that no ABI break can have a place.
Thanks,
Robert Baldyga
next prev parent reply other threads:[~2015-04-09 10:18 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-02 13:13 [PATCH v3 0/4] extcon: usb-gpio: fixes and improvements Robert Baldyga
2015-04-02 13:13 ` [PATCH v3 1/4] extcon: usb-gpio: register extcon device before IRQ registration Robert Baldyga
2015-04-03 0:09 ` Chanwoo Choi
2015-04-02 13:13 ` [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection Robert Baldyga
2015-04-02 14:02 ` Roger Quadros
2015-04-09 2:12 ` Chanwoo Choi
2015-04-09 7:57 ` Robert Baldyga
2015-04-09 9:07 ` Chanwoo Choi
2015-04-09 9:24 ` Robert Baldyga
2015-04-09 9:59 ` Roger Quadros
2015-04-09 10:18 ` Robert Baldyga [this message]
2015-04-10 7:39 ` Chanwoo Choi
2015-04-10 7:17 ` Chanwoo Choi
2015-04-10 7:45 ` Robert Baldyga
2015-04-10 8:10 ` Chanwoo Choi
2015-04-10 8:46 ` Robert Baldyga
2015-04-10 9:18 ` Chanwoo Choi
2015-04-10 9:42 ` Robert Baldyga
2015-04-14 10:01 ` Roger Quadros
2015-04-14 10:02 ` Roger Quadros
2015-04-14 10:31 ` Chanwoo Choi
2015-04-14 10:38 ` Roger Quadros
2015-04-14 11:29 ` Chanwoo Choi
2015-04-15 3:27 ` Peter Chen
2015-04-15 7:50 ` Roger Quadros
2015-04-15 9:26 ` Chanwoo Choi
2015-04-16 1:59 ` Peter Chen
2015-04-16 7:00 ` Chanwoo Choi
2015-04-16 7:13 ` Ivan T. Ivanov
2015-04-16 7:59 ` Chanwoo Choi
2015-04-16 8:01 ` Peter Chen
2015-04-16 8:26 ` Chanwoo Choi
2015-04-30 7:32 ` Roger Quadros
2015-04-30 7:55 ` Chanwoo Choi
2015-04-30 8:04 ` Roger Quadros
2015-04-16 7:59 ` Peter Chen
2015-04-16 7:16 ` Roger Quadros
2015-04-02 13:13 ` [PATCH v3 3/4] extcon: usb-gpio: make debounce value configurable in devicetree Robert Baldyga
2015-04-02 13:13 ` [PATCH v3 4/4] Documentation: extcon: usb-gpio: update usb-gpio binding description Robert Baldyga
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