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.c...@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. > >> >>> 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
