Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754529AbbDNKC6 (ORCPT ); Tue, 14 Apr 2015 06:02:58 -0400 Received: from devils.ext.ti.com ([198.47.26.153]:44915 "EHLO devils.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753835AbbDNKCt (ORCPT ); Tue, 14 Apr 2015 06:02:49 -0400 Message-ID: <552CE5C0.3010207@ti.com> Date: Tue, 14 Apr 2015 13:02:40 +0300 From: Roger Quadros User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 MIME-Version: 1.0 To: Chanwoo Choi , Robert Baldyga CC: , , , , , "Balbi, Felipe" , "ABRAHAM, KISHON VIJAY" , Peter Chen Subject: Re: [PATCH v3 2/4] extcon: usb-gpio: add support for VBUS detection References: <1427980385-21285-1-git-send-email-r.baldyga@samsung.com> <1427980385-21285-3-git-send-email-r.baldyga@samsung.com> <5525E012.5050207@samsung.com> <552630E4.9030309@samsung.com> <55264148.8070903@samsung.com> <55264534.4020006@samsung.com> <55277910.2070000@samsung.com> <55277FA2.6090700@samsung.com> <55278580.2090809@samsung.com> <55278DD3.3020409@samsung.com> <55279550.1060609@samsung.com> <552CE579.6060702@ti.com> In-Reply-To: <552CE579.6060702@ti.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5428 Lines: 133 Fixed Kishon's id. On 14/04/15 13:01, Roger Quadros wrote: > 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@vger.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@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/