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Date: Tue, 14 Apr 2015 13:01:29 +0300 From: Roger Quadros <rogerq@...com> To: Chanwoo Choi <cw00.choi@...sung.com>, Robert Baldyga <r.baldyga@...sung.com> CC: <myungjoo.ham@...sung.com>, <linux-usb@...r.kernel.org>, <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <m.szyprowski@...sung.com>, "Balbi, Felipe" <balbi@...com>, <kishon@...comg>, Peter Chen <peter.chen@...escale.com> Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection On 10/04/15 12:18, Chanwoo Choi wrote: > On 04/10/2015 05:46 PM, Robert Baldyga wrote: >> On 04/10/2015 10:10 AM, Chanwoo Choi wrote: >>> On 04/10/2015 04:45 PM, Robert Baldyga wrote: >>>> On 04/10/2015 09:17 AM, Chanwoo Choi wrote: >>>>> Hi Robert, >>>>> >>>>> On 04/09/2015 06:24 PM, 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. >>>>>>> >>>>>>> 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 >>>>> >>>>> As I knew, USB OTG port don't send the attached cable of both USB and USB-HOST >>>>> at the same time. The case3 in your patch update two cable state about one h/w port. >>>>> >>>> >>>> It's because simple "USB" or "USB-HOST" means nothing for USB OTG >>>> machine. It needs to know exact VBUS and ID states, which cannot be >>>> concluded basing on cable type only. That's why I have used "USB-HOST" >>>> name together with "USB" to pass additional information about USB cable >>>> connection. >>> >>> I think this method is not proper to support this case. >>> It may cause the confusion about other case using USB/USB-HOST cable state >>> except of you commented case. >> >> That's why I finally proposed to use "USB-ID" and "USB-VBUS" in parallel >> with old names. It seems to be simpler solution than adding new >> mechanism notifying about VBUS and ID states changes. > > > As I commented on previous reply, I don't agree to use 'USB-ID' and 'USB-VBUS'. > If we add new strange 'USB-ID' and 'USB-VBUS' name, we would add non-general cable > name continuoulsy. > > I think that extcon core provide the helper API to get the value of VBUS. > But I need to consider it. Now it is starting to look like existing extcon states are not suitable for USB/PHY drivers to deliver VBUS and ID information reliably. This is because based on your comments the "USB" and "USB-HOST" states look like some fuzzy states and have no direct correspondence with "VBUS" and "ID". The fact that they can't become attached simultaneously makes me conclude that "USB" and "USB-HOST" cable states are really capturing only the ID pin state. I can suggest the following options a) let "USB" and "USB-HOST" only indicate ID pin status. Add a new cable state for "VBUS" notification. Maybe call it "USB-POWER" or something. NOTE: "USB-POWER" can become attached simultaneously with "USB" or "USB-HOST". But "USB-POWER" is now really a different cable like "Fast-Charger" or "Slow-Charger". b) stop using extcon framework for USB VBUS and ID notification. cheers, -roger > >> >>> >>>> >>>>> I don't agree. >>>>> >>>>>> that. As I wrote, current USB cable names are misleading. It would be >>>>>> better to have "USB-VBUS" and "USB-ID". >>>>> >>>>> It is strange cable name. I prefer to use only 'USB' cable name. >>>>> But, we could support the other method to get the state of whether USB-VBUS or USB-ID >>>>> by using helper API or others. >>>>> >>>> >>>> Ok, so do you have any idea how to do it? Do we want to supply >>>> additional API for notifying about VBUS and ID changes? >>> >>> No, we need to consider more standard solution to support this case. >>> >> >> Thanks, >> Robert Baldyga >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in >> the body of a message to majordomo@...r.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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