From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0C699C433F5 for ; Thu, 17 Feb 2022 03:44:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232951AbiBQDpJ (ORCPT ); Wed, 16 Feb 2022 22:45:09 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:34872 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232910AbiBQDpI (ORCPT ); Wed, 16 Feb 2022 22:45:08 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D116829C137; Wed, 16 Feb 2022 19:44:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender :Reply-To:Content-ID:Content-Description; bh=QKExgNQWp3Zssh/nqG6fZnwPbmQE7iVXyRjvlEzqCoM=; b=F55Xyk13rPLqv1D0CWn92CH/go LF2wtY8At3qADfgJr/QBA9S0q/xNksDEWXHlT149de660uf8Bu628/FJjVgRF5DvHycjQ/Jj6NuaZ 8AkXiOLnrNiXlrJNtSR02rB6CVWOGtUYmGxqG7Z+z58s9qkvEh5Bh6Q4zkmbuhZhPPSa6B+S74ZqY mlUwQ2AQgz1h4fCmVVOgAJ+rJ5g2IfhewPR2fzipz9jQHzI7jmJ9AAzZHYbqMMc1tSz7SmhXVssAa YBtn8SWkOS/MtBbLXid3p3mr0/9oCT9T4JTt4XEgRPlrLUG0sTZmzFv5l214mrNUsuTr8vFvxjJIl PFXqMU1Q==; Received: from [2601:1c0:6280:3f0::aa0b] by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nKXij-00FHCo-1j; Thu, 17 Feb 2022 03:44:41 +0000 Message-ID: <3f657ffc-e137-de8f-c89e-90676bc42448@infradead.org> Date: Wed, 16 Feb 2022 19:44:35 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.6.0 Subject: Re: earlyprintk=xdbc seems broken Content-Language: en-US To: Dave Hansen , Sven Schnelle , Peter Zijlstra Cc: Mathias Nyman , Greg KH , Lu Baolu , x86@kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Chunfeng Yun References: <88f466ff-a065-1e9a-4226-0abe2e71b686@linux.intel.com> <972a0e28-ad63-9766-88da-02743f80181b@intel.com> From: Randy Dunlap In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/25/22 08:24, Dave Hansen wrote: > On 1/25/22 05:09, Sven Schnelle wrote: >>> Now the documentation states we need this super speed A<->A cable, but >>> could you also update the documentation for usb-c ? There's a fair >>> number of usb-c only devices out there now. >> Stupid beginners question: Would every USB3 A-A cable work, or are the >> debug cables special? I've read the RX/TX pairs have to be swapped, but >> to me it looks like that's always the case? > > My understanding is that the 5v line is disconnected.  Here's one cable I have: > >> https://designintools.intel.com/SVT_DCI_DbC2_3_A_to_A_Debug_Cable_1_Meter_p/itpdciamam1m.htm > > I think they snip that line to prevent any chance of current flowing between devices.  The cable isn't expensive, but I do remember being astounded at how much Intel charged itself for shipping it. ;) This one works OK: https://www.datapro.net/products/usb-3-0-super-speed-a-a-debugging-cable.html > That said, I've also used the same cable Peter has: just a cheap A-to-A cable I had lying around.  It surely has VBUS connected, so I usually plumb it through a USB hub with a power switch.  This surely isn't the "right" way to do it, but it does seem to work in some situations. -- ~Randy