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    SubjectRe: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection
    On 04/14/2015 07:38 PM, Roger Quadros wrote:
    > On 14/04/15 13:31, Chanwoo Choi wrote:
    >> On 04/14/2015 07:02 PM, Roger Quadros wrote:
    >>> Fixed Kishon's id.
    >>>
    >>> On 14/04/15 13:01, Roger Quadros wrote:
    >>>> On 10/04/15 12:18, Chanwoo Choi wrote:
    >>>>> On 04/10/2015 05:46 PM, Robert Baldyga wrote:
    >>>>>> On 04/10/2015 10:10 AM, Chanwoo Choi wrote:
    >>>>>>> On 04/10/2015 04:45 PM, Robert Baldyga wrote:
    >>>>>>>> On 04/10/2015 09:17 AM, Chanwoo Choi wrote:
    >>>>>>>>> Hi Robert,
    >>>>>>>>>
    >>>>>>>>> On 04/09/2015 06:24 PM, 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.
    >>>>>>>>>>>
    >>>>>>>>>>> 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
    >>>>>>>>>
    >>>>>>>>> As I knew, USB OTG port don't send the attached cable of both USB and USB-HOST
    >>>>>>>>> at the same time. The case3 in your patch update two cable state about one h/w port.
    >>>>>>>>>
    >>>>>>>>
    >>>>>>>> It's because simple "USB" or "USB-HOST" means nothing for USB OTG
    >>>>>>>> machine. It needs to know exact VBUS and ID states, which cannot be
    >>>>>>>> concluded basing on cable type only. That's why I have used "USB-HOST"
    >>>>>>>> name together with "USB" to pass additional information about USB cable
    >>>>>>>> connection.
    >>>>>>>
    >>>>>>> I think this method is not proper to support this case.
    >>>>>>> It may cause the confusion about other case using USB/USB-HOST cable state
    >>>>>>> except of you commented case.
    >>>>>>
    >>>>>> That's why I finally proposed to use "USB-ID" and "USB-VBUS" in parallel
    >>>>>> with old names. It seems to be simpler solution than adding new
    >>>>>> mechanism notifying about VBUS and ID states changes.
    >>>>>
    >>>>>
    >>>>> As I commented on previous reply, I don't agree to use 'USB-ID' and 'USB-VBUS'.
    >>>>> If we add new strange 'USB-ID' and 'USB-VBUS' name, we would add non-general cable
    >>>>> name continuoulsy.
    >>>>>
    >>>>> I think that extcon core provide the helper API to get the value of VBUS.
    >>>>> But I need to consider it.
    >>>>
    >>>> Now it is starting to look like existing extcon states are not suitable for USB/PHY drivers to deliver
    >>>> VBUS and ID information reliably.
    >>>> This is because based on your comments the "USB" and "USB-HOST" states look like some fuzzy states
    >>>> and have no direct correspondence with "VBUS" and "ID". The fact that they can't become
    >>>> attached simultaneously makes me conclude that "USB" and "USB-HOST" cable states are really
    >>>> capturing only the ID pin state.
    >>>>
    >>>> I can suggest the following options
    >>>> a) let "USB" and "USB-HOST" only indicate ID pin status. Add a new cable state for "VBUS" notification.
    >>>> Maybe call it "USB-POWER" or something.
    >>
    >> We must discuss it before using the new cable name
    >> such as "USB-POWER", "USB-ID" and "USB-VBUS".
    >
    > I didn't say to add "USB-ID" or "USB-VBUS". solution (a) was to have the following

    Right. Robert suggested the "USB-ID" and "USB-VBUS" cable name on previous mail in mail thread.

    > "USB" - attached means ID is high. i.e. Type-B plug attached.
    > "USB-HOST" - attached means ID is low. i.e. Type-A plug attached.
    > "USB-POWER" - attached means USB power is present. i.e. VBUS is alive.
    >
    > This way the definition of USB and USB-HOST remain true to their name and avoid further confusions.
    > VBUS state is got through the "USB-POWER" cable state.

    There is the same case for MHL cable.
    Also, MHL cable could be connected to VBUS line.
    - MHL : attached just MHL cable.
    - MHL-POWER : attache MHL cable which is connected with VBUS line.

    We must need the opinion of USB/PHY driver's maintainer.

    >
    >>
    >> What is the appropriate method of following two solution?
    >> - Fisrt, use the new cable name "USB-*".
    > I explained this above.
    >
    >> - Second, use the additional API to get the VBUS state.
    >
    > You keep mentioning additional API for VBUS. But I don't see any such API. Can you please
    > suggest what API you are talking about?

    I'm considering following functions for VBUS state. But it is my opinion,
    If USB/PHY drivers's maintainers don't agree the new cable ("USB-POWER"),
    We could use the following function to get VBUS state.
    Because new cable name will affect the USB/PHY drivers.
    - int extcon_{get|set}_vbus_state(struct extcon_dev *edev);

    Cheers,
    Chanwoo Choi


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