Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934761AbcLMTbK (ORCPT ); Tue, 13 Dec 2016 14:31:10 -0500 Received: from mail-oi0-f42.google.com ([209.85.218.42]:32780 "EHLO mail-oi0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933418AbcLMT3h (ORCPT ); Tue, 13 Dec 2016 14:29:37 -0500 MIME-Version: 1.0 In-Reply-To: References: <1481612990-23409-6-git-send-email-john.stultz@linaro.org> From: John Stultz Date: Tue, 13 Dec 2016 11:23:03 -0800 Message-ID: Subject: Re: [RFC][PATCH 5/5] usb: dwc2: Add a quirk to allow speed negotiation for Hisilicon Hi6220 To: Alan Stern 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 , Linux USB List Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1334 Lines: 32 On Tue, Dec 13, 2016 at 5:24 AM, Alan Stern wrote: > 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 If your interested in details, page 12 of the pdf here has some details: https://github.com/96boards/documentation/blob/master/ConsumerEdition/HiKey/AdditionalDocs/HiKey_Hardware_User_Manual_Rev0.2.pdf There's also schematics for the board available (if you are interested in that sort of stuff). You can find the USB bits on Page 4 here: https://github.com/96boards/documentation/blob/master/ConsumerEdition/HiKey/HardwareDocs/HiKey_schematics_LeMaker_version_Rev_A1.pdf > 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? Yes. It drops back to full-speed. thanks -john