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 D178AC433EF for ; Tue, 25 Jan 2022 16:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346074AbiAYQ1J (ORCPT ); Tue, 25 Jan 2022 11:27:09 -0500 Received: from mga18.intel.com ([134.134.136.126]:7382 "EHLO mga18.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346982AbiAYQZF (ORCPT ); Tue, 25 Jan 2022 11:25:05 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1643127900; x=1674663900; h=message-id:date:mime-version:to:cc:references:from: subject:in-reply-to:content-transfer-encoding; bh=pNEbnyLY+nXYgDriBYJiuh8SeETuEBNnzcAZaqb18Wc=; b=BiS1mqoW3n02JZW+jM7VYdA+YpmP3HnO6JoNva4wFejWMiiQMuALIygv 8kcpjU8mq+XqwsjpolODln5WwBQldrdCc/qYDcqQQyq8xmWJiPxc4H1Vk gnOFv+GKk1XWYqR4yEVyHGjhUCW9zQVr+jRHBxZ/ZOp//dQARqdAfoY+l 9KLPoidUfpote6hs1VcEcbUbVkMc34Wy1y0Vh1dDsm80IbChGtTyAXYjB 0hpaefp6fOdyOTzfdgY+gL/UjQUbWjI+X85IQWX6r+Tgd5AqF6aIZ3n0J eKPzf+Zf+bMkJ7RWEv4Juc9weedkfw/m6aUwnzdG9mT4kHODJzrr2CXKm w==; X-IronPort-AV: E=McAfee;i="6200,9189,10237"; a="229918373" X-IronPort-AV: E=Sophos;i="5.88,315,1635231600"; d="scan'208";a="229918373" Received: from orsmga006.jf.intel.com ([10.7.209.51]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2022 08:24:56 -0800 X-IronPort-AV: E=Sophos;i="5.88,315,1635231600"; d="scan'208";a="479552819" Received: from jfink-mobl.amr.corp.intel.com (HELO [10.209.2.7]) ([10.209.2.7]) by orsmga006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2022 08:24:56 -0800 Message-ID: Date: Tue, 25 Jan 2022 08:24:53 -0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Content-Language: en-US To: 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: Dave Hansen Subject: Re: earlyprintk=xdbc seems broken In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. ;) 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.