From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752020AbdAYOih (ORCPT ); Wed, 25 Jan 2017 09:38:37 -0500 Received: from bombadil.infradead.org ([65.50.211.133]:37444 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751897AbdAYOif (ORCPT ); Wed, 25 Jan 2017 09:38:35 -0500 Date: Wed, 25 Jan 2017 15:38:29 +0100 From: Peter Zijlstra To: Lu Baolu Cc: Ingo Molnar , 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 Subject: Re: [PATCH v5 1/4] usb: dbc: early driver for xhci debug capability Message-ID: <20170125143829.GS6515@twins.programming.kicks-ass.net> References: <1479189731-2728-2-git-send-email-baolu.lu@linux.intel.com> <20170119093743.GC22865@gmail.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <588899BA.7040108@linux.intel.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? If there is an error other than !ready, I would expect the hardware to inform you of this through another status bit, no? So why can't you poll indefinitely for either ready or error?