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 A533FC433EF for ; Tue, 25 Jan 2022 13:56:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357426AbiAYN4V (ORCPT ); Tue, 25 Jan 2022 08:56:21 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57848 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358916AbiAYNyO (ORCPT ); Tue, 25 Jan 2022 08:54:14 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90A0AC06174E; Tue, 25 Jan 2022 05:54:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=R97F4j2vJPpYP2hkOl7KqnbnzY+rMR+5Vc9jNgI1Gyc=; b=gYEvOrUjTJSh5whtbj2sO5ibO+ mzZsse1aw+8QOEcsxOrS1e0h39BHF0RSokv9V7dg/Esy4R8yabHdPyCfdU0cgLsgmUli/ramkIQrY KoyXTRGtJ6eOXH1NPbEhAZdQnLixypIXtKCB+OWp11PcjynzEqRpviAQpjcPjYjVrV/F7/NK3/IOF eaxKPE0zkjKTQAblFvsUVUbYwTWaJNXuo23miDHs/q2xoBYrndC6PvkGKAFafC2lXdjkokx620xMM JEQqgzhOJQm5qALCRM1wSqlKr1r8KvIT5Z7O/JXlH+9nMcP/0MN9h/lLl/SqLCMkPG1kcaBlr1cTh M89L7Lng==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nCMGp-002tCJ-3M; Tue, 25 Jan 2022 13:54:03 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id BC1C63002C5; Tue, 25 Jan 2022 14:54:01 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 740C32B37A003; Tue, 25 Jan 2022 14:54:01 +0100 (CET) Date: Tue, 25 Jan 2022 14:54:01 +0100 From: Peter Zijlstra To: Sven Schnelle Cc: Mathias Nyman , Greg KH , Dave Hansen , Lu Baolu , x86@kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Chunfeng Yun Subject: Re: earlyprintk=xdbc seems broken Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Tue, Jan 25, 2022 at 02:09:18PM +0100, Sven Schnelle wrote: > Peter Zijlstra writes: > > > 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? I'm using a random USB3 A-A cable (it came with an HDMI frame grabber of of AliExpress). The official one has a wire missing I think, to avoid ground loops or something like that. The easiest thing to do is try the runtime DBC option: echo enable > /sys/bus/pci/devices/0000:00:14.0/dbc If that works you can see what it takes to make the earlyprintk one working. This thread seems to have much of that covered.