Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932792AbcLMNYO (ORCPT ); Tue, 13 Dec 2016 08:24:14 -0500 Received: from netrider.rowland.org ([192.131.102.5]:35383 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751567AbcLMNYJ (ORCPT ); Tue, 13 Dec 2016 08:24:09 -0500 Date: Tue, 13 Dec 2016 08:24:08 -0500 (EST) From: Alan Stern X-X-Sender: stern@netrider.rowland.org To: John Stultz cc: lkml , Chen Yu , Wei Xu , Guodong Xu , Amit Pundir , Rob Herring , John Youn , Douglas Anderson , Kishon Vijay Abraham I , Felipe Balbi , Greg Kroah-Hartman , Subject: Re: [RFC][PATCH 5/5] usb: dwc2: Add a quirk to allow speed negotiation for Hisilicon Hi6220 In-Reply-To: <1481612990-23409-6-git-send-email-john.stultz@linaro.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 726 Lines: 19 On Mon, 12 Dec 2016, John Stultz wrote: > From: Chen Yu > > The Hi6220's usb controller is limited in that it does not > support "Split Transactions", so it does not support communicating > with low-speed and full-speed devices behind a high-speed hub. > > Thus it requires a quirk so that we can manually drop the usb > speed when low/full-speed are attached, and bump back to high > speed when they are removed. Just out of curiosity (I know nothing about this hardware), what happens if there is a high-speed hub plugged into the host controller and both a high-speed and a full-speed device plugged into the hub? Do you end up forcing the high-speed device to run at full speed? Alan Stern