On 04/09/2015 11:59 AM, Roger Quadros wrote: > Hi, > > 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, >>>>> >>> >>> [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. > > At least for the kernel users [1] 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). > > [1] > - drivers/usb/phy/phy-omap-otg.c > - drivers/usb/dwc3/dwc3-omap.c > > >>> >>> 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? > We can also leave USB and USB-HOST as "dummy cable detection states", like they currently are, and add new USB-VBUS and USB-ID cables without removing the old ones. It will cause some redundancy, but will make us sure, that no ABI break can have a place. Thanks, Robert Baldyga -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
