From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755417Ab1I2Kjw (ORCPT ); Thu, 29 Sep 2011 06:39:52 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:60451 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750870Ab1I2Kjv (ORCPT ); Thu, 29 Sep 2011 06:39:51 -0400 Date: Thu, 29 Sep 2011 11:39:39 +0100 From: Will Deacon To: Russell King - ARM Linux Cc: Stephen Boyd , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , David Brown Subject: Re: [PATCHv2 2/2] ARM: debug: Move DEBUG_ICEDCC into the DEBUG_LL choice Message-ID: <20110929103939.GD25061@e102144-lin.cambridge.arm.com> References: <1316568208-4518-1-git-send-email-sboyd@codeaurora.org> <1316568208-4518-2-git-send-email-sboyd@codeaurora.org> <4E83D25C.6020306@codeaurora.org> <20110929092102.GB25061@e102144-lin.cambridge.arm.com> <20110929094243.GC25061@e102144-lin.cambridge.arm.com> <20110929094602.GH23944@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110929094602.GH23944@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Russell, On Thu, Sep 29, 2011 at 10:46:02AM +0100, Russell King - ARM Linux wrote: > On Thu, Sep 29, 2011 at 10:42:43AM +0100, Will Deacon wrote: > > Bah, just took this for a spin on my Realview-PBX (Cortex-A9) platform and > > the board won't boot unless I have a hardware debugger enabled that can > > service the comms channel. This contradicts the Kconfig text which says: > > > > It does include a timeout to ensure that the system does not > > totally freeze when there is nothing connected to read. > > > > so we certainly need to fix something! > > One of the problems you'll encounter is that there's places where we > don't have any timer infrastructure (eg, decompressor) and software > timing loops won't work (they'll be too slow for the lower-end CPUs > and too fast for the upper-end CPUs.) Agreed, software timing loops are the only option and it's impossible to get them right everywhere. I think the Kconfig help text should be updated so that the timeout paragraph is removed. > The best fix is probably to leave that as-is, but introduce a 'default' > output entry instead - so platforms which don't have any listed will > get that instead of the ICEDDC stuff. Ok. Rather than 'default' (which people will probably select in preference to choosing the correct UART) how about something like below? I can split this into two patches if you prefer. Will ----8<---- diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug index 32b1be4..bfdf86b 100644 --- a/arch/arm/Kconfig.debug +++ b/arch/arm/Kconfig.debug @@ -81,6 +81,14 @@ choice prompt "Kernel low-level debugging port" depends on DEBUG_LL + config DEBUG_LL_UART_NONE + bool "No low-level debugging UART" + help + Say Y here if your platform doesn't provide a UART option + below. This relies on your platform choosing the right UART + definition internally in order for low-level debugging to + work. + config DEBUG_ICEDCC bool "Kernel low-level debugging via EmbeddedICE DCC channel" help @@ -89,8 +97,8 @@ choice co-processor 14. This is known to work on the ARM9 style ICE channel and on the XScale with the PEEDI. - It does include a timeout to ensure that the system does not - totally freeze when there is nothing connected to read. + Note that this may cause the system to hang during boot if + there is nothing to read from the DCC. config DEBUG_FOOTBRIDGE_COM1 bool "Kernel low-level debugging messages via footbridge 8250 at PCI COM1"