Hi Guenter, On 2016년 08월 04일 23:47, Guenter Roeck wrote: > On Thu, Aug 4, 2016 at 3:57 AM, Chanwoo Choi <cw00.c...@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.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. >> > > 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.
OK. I'll drop the EXTCON_PROP_USB_ID. Thanks. Regards, Chanwoo Choi > > 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 >> > > >
