From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932580AbcHDI5S (ORCPT ); Thu, 4 Aug 2016 04:57:18 -0400 Received: from bear.ext.ti.com ([198.47.19.11]:52361 "EHLO bear.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754047AbcHDI5D (ORCPT ); Thu, 4 Aug 2016 04:57:03 -0400 Subject: Re: [PATCH v3 2/6] extcon: Add the support for extcon property according to extcon type To: Guenter Roeck , Chanwoo Choi References: <1470103105-5992-1-git-send-email-cw00.choi@samsung.com> <1470103105-5992-3-git-send-email-cw00.choi@samsung.com> <1c9b6c33-5699-2767-f97c-d14fb0db7ec6@ti.com> <57A05501.8040508@samsung.com> <47c543d6-0d2d-ffe9-6d81-4773eef46729@ti.com> <57A28F8F.7010101@samsung.com> CC: linux-kernel , Felipe Balbi , , Chris Zhong , Guenter Roeck , , Krzysztof Kozlowski From: Roger Quadros Message-ID: <565b50ac-7b34-740f-ca59-88c3b95bfe82@ti.com> Date: Thu, 4 Aug 2016 11:49:36 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/08/16 07:09, Guenter Roeck wrote: > On Wed, Aug 3, 2016 at 5:42 PM, Chanwoo Choi 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. > >> 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. cheers, -roger