Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754577AbdLHQCs (ORCPT ); Fri, 8 Dec 2017 11:02:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47098 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754363AbdLHQCn (ORCPT ); Fri, 8 Dec 2017 11:02:43 -0500 Subject: Re: [PATCH 0/2] acpi, x86: Add SPCR table support To: Jeffrey Hugo , Ingo Molnar References: <20171207172912.17868-1-prarit@redhat.com> <20171208062925.64ov23u7oxmdfzyk@gmail.com> Cc: Jonathan Corbet , x86@kernel.org, linux-pm@vger.kernel.org, Catalin Marinas , Bhupesh Sharma , linux-doc@vger.kernel.org, Will Deacon , linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, Ingo Molnar , "Rafael J. Wysocki" , Lv Zheng , linux-serial@vger.kernel.org, "H. Peter Anvin" , Thomas Gleixner , linux-arm-kernel@lists.infradead.org From: Prarit Bhargava Message-ID: Date: Fri, 8 Dec 2017 11:02:40 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Fri, 08 Dec 2017 16:02:42 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3394 Lines: 89 On 12/08/2017 10:31 AM, Jeffrey Hugo wrote: > On 12/8/2017 7:29 AM, Prarit Bhargava wrote: >> >> >> On 12/08/2017 01:29 AM, Ingo Molnar wrote: >>> >>> * Prarit Bhargava wrote: >>> >>>> The SPCR (Serial Port Console Redirection) Table provides information >>>> about the configuration of serial port. This information can be used >>>> to configure the early console. >>> >>> s/about the configuration of serial port >>> /about the configuration of the serial port >>> >>>> SPCR support was added for arm64 and is made available across all arches >>>> in this patchset. The first patch adds a weak per-arch configuration function >>>> and moves the SPCR code into ACPI. The second patch adds support to x86. >>>> >>>> The existing behaviour on arm64 is maintained. If the SPCR exists the >>>> earlycon and console are automatically configured. >>> >>> s/arm64 >>> /ARM64 >>> >>> which is easier to read and it's also the prevalent spelling: >>> >>> triton:~/tip> for N in $(git grep -ih arm64 arch/arm64/ | sed >>> 's/[[:punct:]]/ /g'); do echo $N | grep -iw arm64; done | sort | uniq -c >>> 412 arm64 >>> 1 Arm64 >>> 854 ARM64 >>> >>>> The existing default behaviour on x86 is also maintained. If no console or >>>> earlycon parameter is defined and the SPCR exists , the serial port is not >>>> configured. If the earlycon parameter is used both the early console >>>> and the console are configured using the data from the SPCR. >>> >>> s/exists , the >>> /exists, the >>> >>> But, the logic to not use the SPCR looks confusing to me. >>> >>> The SPCR is only present if the user has explicitly configured a serial console >>> for that machine, either in the firmware, or remotely via IPMI, correct? I.e. >>> SPCR >>> will not be spuriously present by default on systems that have a serial console >>> but the user never expressed any interest for them, right? >> >> If I disable "Serial Port Console Debug" in my BIOS I still see the SPCR >> configured: >> >> [root@prarit-lab ~]# dmesg | grep SPCR >> [ 0.000000] ACPI: SPCR 0x0000000069031000 000050 (v01 >> 00000000 00000000) >> >> AFAICT the SPCR is always enabled on some systems. > > "Serial Port Console Debug" sounds like DBG2 to me, although I am unsure of the > specific platform you are referencing. > >> >>> >>> If so then we should pick up that serial console configuration and activate it, >>> regardless of any kernel boot options! >> >> I'm worried about someone who doesn't want a console on ttyS0 suddenly ending up >> with one. The SPCR could contain incorrect data, etc. >> >> I originally wanted this on by default, but the chances of breaking someone's >> setup seems significant doesn't it? Maybe I'm being too cautious. Anyone else >> want to weigh in? I'm not ignoring your idea Ingo, I'm just worried about being >> yelled at by a user :) because I broke their default console setup. >> > > SPCR is always present on QDF2400 (ARM64 platform). Firmware will automatically > update the SPCR table to point to the correct console (IE Serial-over-LAN or SOL > if configured via IPMI). Unless a user specifically chooses to override the > SPCR via "console=", we expect that a console will be present based on the data > in SPCR. Hey Jeffrey -- I think Ingo's & my conversation is x86-specific. I am *NOT* changing the behaviour on ARM64. P. >