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 E75FAC43217 for ; Tue, 25 Jan 2022 17:19:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1454469AbiAYRTU (ORCPT ); Tue, 25 Jan 2022 12:19:20 -0500 Received: from mga11.intel.com ([192.55.52.93]:16098 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1453635AbiAYRPh (ORCPT ); Tue, 25 Jan 2022 12:15:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1643130937; x=1674666937; h=to:cc:references:from:subject:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=veCZt3yQfTYBk3+GU00z9OZ21bMHmTBnTb5ztruHxPg=; b=InZJhdZ8h/rTgZAng4zAvgPPOxOIYUdsBTyj+fZhOlTEjgwwWVQEmyN/ mChuqpKxs5FvXyAxIlJI1gyK/Y7QQDKkOTRywTXb2wboEjniD5VqYBaRN mil6iXBqEnpVNfe2314Eyx7ak5juYnCTRo/8Smt7+jGYVyPoEKsIEfxoI s1l6NB6V37lsFm4TBmQtPlyRrvmK6+3eo9WvnJvEezIJNkrYVla0xySS6 +rTIix+gbWWfd3smRQf4z8bEr/v5gBZZm6bvwo6vCI+Vmgpg2fBclujey +ani0HDY3D3gCt8+GvJYyQWOnylpHrvjlbipGC2vWZH0IZn0yoRpgQ3mL g==; X-IronPort-AV: E=McAfee;i="6200,9189,10237"; a="243951946" X-IronPort-AV: E=Sophos;i="5.88,315,1635231600"; d="scan'208";a="243951946" Received: from orsmga001.jf.intel.com ([10.7.209.18]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 25 Jan 2022 09:11:37 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.88,315,1635231600"; d="scan'208";a="563104854" Received: from mattu-haswell.fi.intel.com (HELO [10.237.72.199]) ([10.237.72.199]) by orsmga001.jf.intel.com with ESMTP; 25 Jan 2022 09:11:33 -0800 To: Sven Schnelle , Peter Zijlstra Cc: Greg KH , Dave Hansen , Lu Baolu , x86@kernel.org, linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org, Chunfeng Yun References: From: Mathias Nyman Subject: Re: earlyprintk=xdbc seems broken Message-ID: Date: Tue, 25 Jan 2022 19:13:03 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25.1.2022 16.01, Sven Schnelle wrote: > Peter Zijlstra writes: > >> 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. > > Thanks, the sysfs test works for me. I have two A-A cables, one is from > a cheap PCI-e extender, the other one from a KVM switch. Both work, > which is great. So i assume that most A-A cable would work. I'm building > a new kernel now with the patch on top, lets see. > I enabled runtime dbc on a Tigerlake 0000:00:0d.0 xhci, and connected the USB-C port to a host using a USB-C to A adapter, and a cheap USB3 A-to-A cable. Worked for me, but can't make any official recommendation. I'm guessing the USB-C port works as long as the USB-C TX/RX pins are muxed to a xhci. With additional dbc patches it's possible to have dbc connected on both xhci controllers at the same time (runtime via sysfs). -Mathias