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? cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
