Messages in this thread | | | From | Guenter Roeck <> | Date | Thu, 4 Aug 2016 07:47:28 -0700 | Subject | Re: [PATCH v3 2/6] extcon: Add the support for extcon property according to extcon type |
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On Thu, Aug 4, 2016 at 3:57 AM, Chanwoo Choi <cw00.choi@samsung.com> wrote: > Hi Guenter and Roger, > > On 2016년 08월 04일 17:49, Roger Quadros wrote: >> On 04/08/16 07:09, Guenter Roeck wrote: >>> On Wed, Aug 3, 2016 at 5:42 PM, Chanwoo Choi <cw00.choi@samsung.com> wrote: >>>> Hi Roger, >>>> >>>> On 2016년 08월 03일 18:46, Roger Quadros wrote: >>>>> Hi Chanwoo, >>>>> >>> >>> [ ... ] >>> >>>>>>>> + /* >>>>>>>> + * Check whether the external connector is attached. >>>>>>>> + * If external connector is detached, the user can not >>>>>>>> + * get the property value. >>>>>>>> + */ >>>>>>> >>>>>>> How will this work for USB case? We need to know VBUS and ID states >>>>>>> even if the USB cable is detached. >>>>>> >>>>>> When USB is detached, extcon_get_property return the default value without any operation. >>>>>> The default value of supported property are 0 (zero). If new property need the differnt default >>>>>> value, I'll support it. >>>>> >>>>> Is the property a property of the connector or of the cable? >>>>> >>>>> In my opinion, ID and VBUS are properties of the USB connector and not of >>>>> the USB cable. So extcon must provide valid status for those properties >>>>> even if USB cable or USB_HOST cable is detached. >>>> >>>> I don't understand about that if USB and USB_HOST are detached, >>>> how can the USB be operating? As you mentioned that, extcon must >>>> provide the valid status for both state and properties. >>>> >>> >>> Correct. No cable means that the polarity is unknown, and VBUS must not be >>> active (for USB_HOST), or it can not be active (for USB). >> >> OK. >> >>> >>> Only question might be EXTCON_PROP_USB_ID; I am not sure I understand >>> what it is supposed to return. Maybe it would be worthwhile to document it ? >> >> Agreed. It seems redundant as ID can be easily inferred from USB_HOST cable state. >> i.e. if USB_HOST is attached ID is 0. If USB_HOST is detached ID is 1. > > Do you mean the EXTCON_PROP_USB_ID is un-needed? > I'll remove the EXTCON_PROP_USB_ID property on next version. >
If ID reflects host vs. device state, yes, it is not needed. Or, alternatively, one of USB and USB_HOST would not be needed if ID is present. Since that is not feasible because it would modify the ABI to user space, dropping ID makes sense.
Thanks, Guenter
>> >>> >>>> So, I already mentioned, When USB and USB_HOST are detached, >>>> extcon return the default value instead of error value. >>>> I think that it is reasonable. Why is it not a valid? >>>> >>> >>> I agree; I don't know what else could be returned if no cable is >>> attached, even if we wanted to. >>> >> OK. >> >> I understood now that if kernel USB driver can interpret EXTCON_USB, EXTCON_USB_HOST >> and VBUS property, it sufficiently captures ID and VBUS information. >> > > Regards, > Chanwoo Choi >
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