Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752708AbdC0Mx4 convert rfc822-to-8bit (ORCPT ); Mon, 27 Mar 2017 08:53:56 -0400 Received: from out.consiagnet.it ([83.149.128.196]:19967 "EHLO out.consiagnet.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752054AbdC0Mxr (ORCPT ); Mon, 27 Mar 2017 08:53:47 -0400 X-Spam-Flag: NO X-Spam-Score: -1.595 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 10.2 \(3259\)) Subject: Re: [PATCH] usb-musb: keep VBUS on when device is disconnected From: Moreno Bartalucci In-Reply-To: <2d10809f-d482-ffa9-30b7-8785e94ab102@gmail.com> Date: Mon, 27 Mar 2017 14:53:27 +0200 Cc: Bin Liu , "linux-omap@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Alessio Igor Bogani Content-Transfer-Encoding: 8BIT Message-Id: <00882633-3F61-4010-A4D2-D04473282B10@tecnorama.it> References: <20170315140801.97230-1-moreno.bartalucci@tecnorama.it> <20170324185836.GC19814@uda0271908> <2d10809f-d482-ffa9-30b7-8785e94ab102@gmail.com> To: Lars Melin X-Mailer: Apple Mail (2.3259) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1093 Lines: 24 > Il giorno 25 mar 2017, alle ore 08:21, Lars Melin ha scritto: > >> >> The usb device has been disconnected, why it still cares about VBUS >> power? > > Morphing devices (3G dongles, wifi dongles, some printers) boots up in install mode, usually only as a virtual cd-rom containing Windows drivers and software. > [...] > why a host only configured port should cut the VBUS supply, it could be always on right? > Yes, that’s exactly the problem I tried to solve with this patch. I have to add that the problem was not there with kernels up to 4.8.17, I started to see it with 4.9 and up. By git-bisecting kernel sources, it appears this behaviour has been introduced by this commit: 2f3fd2c5bde1f94513c3dc311ae64494085ec371 I also agree that, in my opinion, a host only port should never remove the VBUS supply, as it happens on all the PCs (linux+windows+mac) that I tested until now. I saw this problem on a beaglebone black. Of course I’m available to do all the tests that you might suggest me to help you better understand the issue. Moreno Bartalucci