From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A24D653BA for ; Tue, 31 Oct 2023 03:51:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="DqA3DiLE" Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:3::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1C701B3; Mon, 30 Oct 2023 20:51:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20210309; 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=NcJE+muHCTM+F5ydwVKCzS7huTyeARslBg0+emRqTPI=; b=DqA3DiLEz4btMtwydEToDoDcBW pJpoRs+uF5ciYUtRW88W3duync7qDFpXA6gR5jc6RJHo1DZG3s8u6EzwtyP7hFSFOB4JZxP7LWcHC jn0fP3AgSKb8pfUZqRjht9L6tHphFHyFjAyuG2feUTkPKMeXJ+f4+HayiCLkGnKtnBxDGJ70X2OFN pWW7ttkPqVBoh4LTszRABbWARW77Vo4uQbxQpj8tj91QsyVoa9ID38zRtHe46XOMcNzL0bQoR322Y 6681g3cy6ZTKg1O3U+QmV6+RNN/9p90fNNcUt1ZnIBFNTVvjsKK9pGAp89NvN86qKvjGbLusnbic3 KHOsrx3A==; Received: from [50.53.46.231] (helo=[192.168.254.15]) by bombadil.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1qxfmV-004UOn-0j; Tue, 31 Oct 2023 03:51:07 +0000 Message-ID: <842a0d64-279d-4052-a243-95fee608ea76@infradead.org> Date: Mon, 30 Oct 2023 20:51:06 -0700 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: Gaps in logs while using usb-serial as a console To: Alan Stern , Greg KH Cc: ariel marcovitch , johan@kernel.org, linux-usb@vger.kernel.org, Linux Kernel Mailing List References: <2023103052-unpeeled-calibrate-ae48@gregkh> <2023103003-defection-recess-cf49@gregkh> <968c62ca-0ef2-4bf1-a17b-a6d88d5e2e20@rowland.harvard.edu> Content-Language: en-US From: Randy Dunlap In-Reply-To: <968c62ca-0ef2-4bf1-a17b-a6d88d5e2e20@rowland.harvard.edu> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/30/23 07:19, Alan Stern wrote: > On Mon, Oct 30, 2023 at 09:30:15AM +0100, Greg KH wrote: >> On Mon, Oct 30, 2023 at 10:15:30AM +0200, ariel marcovitch wrote: >>>> Please realize that usb-serial console was the result of me loosing a >>>> drunken bet. It's amazing it works at all. For "fake" devices like >>> LOL your drunken bet was quite helpful to some people >>> Because modern PCs come without a serial port, I wanted to use it to >>> see early logs on my crashing kernel without having to use printk >>> delay and things like that. >>> I'm curious as to how kernel people debug PCs in general... >> >> We use a usb debug port connection (it's a special cable). For EHCI it is a special cable. For XHCI you can use a special cable but it is not required. (I saw a few people on LKML say that a normal data cable works so I tested it and it does work.) But if you want the special cable (for XHCI), this one works: https://www.datapro.net/products/usb-3-0-super-speed-a-a-debugging-cable.html So I tested with both the special debug cable and a normal A-A data cable, both with satisfactory results. > Sometimes people use netconsole (see > Documentation/networking/netconsole.rst). I don't know how common it is > nowadays, and it may not be quite as reliable as a debug port device, > but it should still work. And it doesn't require special hardware. It would be great if netconsole worked with wifi and not wired (ethernet). -- ~Randy