Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection
From: Roger Quadros
Date: Thu Apr 09 2015 - 05:59:55 EST
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,
>>>> But, I have one question about case
>>>> 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  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).
>> 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?
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/