From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751015AbdEaD12 (ORCPT ); Tue, 30 May 2017 23:27:28 -0400 Received: from mga03.intel.com ([134.134.136.65]:57089 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750913AbdEaD10 (ORCPT ); Tue, 30 May 2017 23:27:26 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.38,421,1491289200"; d="scan'208";a="1176342138" Subject: Re: [PATCH v8 2/5] usb: early: add driver for xhci debug capability To: Vlastimil Babka , Greg Kroah-Hartman , Ingo Molnar References: <1490083293-3792-1-git-send-email-baolu.lu@linux.intel.com> <1490083293-3792-3-git-send-email-baolu.lu@linux.intel.com> Cc: Mathias Nyman , tglx@linutronix.de, peterz@infradead.org, linux-usb@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, Steven Rostedt From: Lu Baolu Message-ID: <592E3817.4030402@linux.intel.com> Date: Wed, 31 May 2017 11:27:19 +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: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 05/30/2017 09:46 PM, Vlastimil Babka wrote: > On 03/21/2017 09:01 AM, Lu Baolu wrote: >> XHCI debug capability (DbC) is an optional but standalone >> functionality provided by an xHCI host controller. Software >> learns this capability by walking through the extended >> capability list of the host. XHCI specification describes >> DbC in the section 7.6. >> >> This patch introduces the code to probe and initialize the >> debug capability hardware during early boot. With hardware >> initialized, the debug target (system on which this code is >> running) will present a debug device through the debug port >> (normally the first USB3 port). The debug device is fully >> compliant with the USB framework and provides the equivalent >> of a very high performance (USB3) full-duplex serial link >> between the debug host and target. The DbC functionality is >> independent of the xHCI host. There isn't any precondition >> from the xHCI host side for the DbC to work. >> >> One use for this feature is kernel debugging, for example >> when your machine crashes very early before the regular >> console code is initialized. Other uses include simpler, >> lockless logging instead of a full-blown printk console >> driver and klogd. >> >> Cc: Ingo Molnar >> Cc: Mathias Nyman >> Signed-off-by: Lu Baolu > ... > >> + >> +#define XDBC_TRACE >> +#ifdef XDBC_TRACE >> +#define xdbc_trace trace_printk > Did you forget to remove the #define XDBC_TRACE? > > Enabling this driver brings the "trace_printk() being used. Allocating > extra memory. This means that this is a DEBUG kernel and it is unsafe > for production use." message in 4.12-rcX dmesg. This feature is only for a DEBUG kernel, should not be enabled for any production kernel. This was the reason I enabled trace_printk() by default. Best regards, Lu Baolu > Thanks, > Vlastimil >