From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755453Ab2GXXUm (ORCPT ); Tue, 24 Jul 2012 19:20:42 -0400 Received: from ch1ehsobe004.messaging.microsoft.com ([216.32.181.184]:1654 "EHLO ch1outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754997Ab2GXXUk (ORCPT ); Tue, 24 Jul 2012 19:20:40 -0400 X-Forefront-Antispam-Report: CIP:160.33.194.230;KIP:(null);UIP:(null);IPV:NLI;H:usculsndmail03v.am.sony.com;RD:mail.sonyusa.com;EFVD:NLI X-SpamScore: -4 X-BigFish: VPS-4(zzbb2dI98dI9371I1432Izz1202hzzz2fh2a8h668h839hd25hf0ah107ah10d2h) Message-ID: <500F2DB7.50403@am.sony.com> Date: Tue, 24 Jul 2012 16:20:23 -0700 From: Frank Rowand Reply-To: User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.17) Gecko/20110428 Fedora/3.1.10-1.fc14 Thunderbird/3.1.10 MIME-Version: 1.0 To: Arnd Bergmann CC: Catalin Marinas , Christopher Covington , Stephen Warren , "linux-kernel@vger.kernel.org" , Will Deacon , Domenico Andreoli Subject: Re: [08/36] AArch64: Kernel booting and initialisation References: <1341608777-12982-9-git-send-email-catalin.marinas@arm.com> <500DB986.7090309@codeaurora.org> <20120724162404.GB29519@arm.com> <201207241853.16625.arnd@arndb.de> In-Reply-To: <201207241853.16625.arnd@arndb.de> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-OriginatorOrg: am.sony.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/24/12 11:53, Arnd Bergmann wrote: > On Tuesday 24 July 2012, Catalin Marinas wrote: >> On Mon, Jul 23, 2012 at 09:52:22PM +0100, Christopher Covington wrote: >>> Hi Catalin and Stephen, >>> >>> Catalin Marinas - July 8, 2012, 9:18 a.m. >>>> On Fri, Jul 06, 2012 at 10:32:54PM +0100, Stephen Warren wrote: >>>> >>>>> Also, on Tegra at least and perhaps OMAP too, there are a few parts >>>>> of earlyprintk serial port setup (i.e. port selection) which happen >>>>> as part of the decompressor rather than the main kernel image, so >>>>> we'd have to re-jig that too. >>>> >>>> Whatever we did on AArch32, if it was useful and we want to follow a >>>> similar model it needs porting given that the code cannot be shared. So >>>> there is nothing to re-jig but rather implement. >>>> >>>> As for earlyprintk, you can initialise it in the decompressed kernel >>>> anyway. But even though it's a useful debugging tool, it goes against >>>> the single Image aim (at least the current printascii/addruart >>>> implementation). I don't have a proper implementation yet. >>> >>> Would DCC [1] be a reasonably commonly available early printk mechanism >>> for the single image to provide? >> >> Yes, this can be implemented but I think it has its own restrictions, >> requiring a JTAG connection. > > Right, which means that it's not generic and we still need to make > a decision for a how we want to solve the underlying problem. The > options I see are: > > 1. Have no earlyprintk before loading the console drivers > 2. Make the series from Domenico architecture independent code > 3. Reimplement a layer like that, differently > 4. Make it a compile-time option and allow this only for > low level debugging purposes but disable it in distro kernels. I have found earlyprintk to be very valuable for debugging the many times that boot fails for me. Not having earlyprintk does not seem a good idea to me. Option 4 is perfectly acceptable for my use cases. -Frank