From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751938AbdBIHjI (ORCPT ); Thu, 9 Feb 2017 02:39:08 -0500 Received: from mga14.intel.com ([192.55.52.115]:5647 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751775AbdBIHjH (ORCPT ); Thu, 9 Feb 2017 02:39:07 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.35,349,1484035200"; d="scan'208";a="56827189" Subject: Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability To: Ingo Molnar References: <58817A25.6080305@linux.intel.com> <20170122090423.GA15061@gmail.com> <5886DBB7.4070501@linux.intel.com> <20170124082039.GB8667@gmail.com> <5888377F.8090709@linux.intel.com> <20170125092355.GA24580@gmail.com> <20170125095736.GP6515@twins.programming.kicks-ass.net> <588899BA.7040108@linux.intel.com> <20170125143829.GS6515@twins.programming.kicks-ass.net> <5888C986.4020809@linux.intel.com> <20170126072219.GB3399@gmail.com> Cc: Peter Zijlstra , Greg Kroah-Hartman , Mathias Nyman , Ingo Molnar , tglx@linutronix.de, linux-usb@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby From: Lu Baolu Message-ID: <589C1C35.2070604@linux.intel.com> Date: Thu, 9 Feb 2017 15:37:25 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <20170126072219.GB3399@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Ingo, On 01/26/2017 03:22 PM, Ingo Molnar wrote: > * Lu Baolu wrote: > >> Hi, >> >> On 01/25/2017 10:38 PM, Peter Zijlstra wrote: >>> On Wed, Jan 25, 2017 at 08:27:38PM +0800, Lu Baolu wrote: >>>> In my driver, udelay() is mostly used to handle time out. >>>> >>>> Xdbc hides most USB things in its firmware. Early printk driver only needs >>>> to setup the registers/data structures and wait until link ready or time out. >>>> Without udelay(), I have no means to convert the polling times into waiting >>>> time. >>> What is timeout and why? >> Put it in simple: >> >> The driver sets the RUN bit in control register and polls READY >> bit in status register for the successful USB device enumeration. >> As the USB device enumeration might fail and the READY bit will >> never be set, the driver must have a timeout logic to avoid >> endless loop. > Is there any error status available in the host registers anywhere that tells us > that enumeration did not succeed? No, there isn't. The xhci spec requires software to impose a timeout. Page 425, xhci specification: " Software shall impose a timeout between the detection of the Debug Host connection and the DbC Run transition to ‘1’. " Best regards, Lu Baolu