Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751293AbbBGFDs (ORCPT ); Sat, 7 Feb 2015 00:03:48 -0500 Received: from mail-ie0-f176.google.com ([209.85.223.176]:36980 "EHLO mail-ie0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750756AbbBGFDp convert rfc822-to-8bit (ORCPT ); Sat, 7 Feb 2015 00:03:45 -0500 MIME-Version: 1.0 In-Reply-To: <54D5884A.6050009@linaro.org> References: <1422881149-8177-1-git-send-email-hanjun.guo@linaro.org> <1422881149-8177-9-git-send-email-hanjun.guo@linaro.org> <20150202134033.GR4278@bivouac.eciton.net> <20150202135051.GA3825@xora-haswell.xora.org.uk> <20150202163253.GG21175@leverpostej> <54D5884A.6050009@linaro.org> Date: Sat, 7 Feb 2015 05:03:44 +0000 Message-ID: Subject: Re: [PATCH v8 08/21] dt / chosen: Add linux,uefi-stub-generated-dtb property From: Ard Biesheuvel To: Hanjun Guo Cc: G Gregory , Mark Rutland , Leif Lindholm , Mark Langsdorf , "linaro-acpi@lists.linaro.org" , Catalin Marinas , Will Deacon , "wangyijing@huawei.com" , Rob Herring , Lorenzo Pieralisi , Jonathan Corbet , Timur Tabi , Daniel Lezcano , "linux-acpi@vger.kernel.org" , "grant.likely@linaro.org" , Charles Garcia-Tobin , "phoenix.liyi@huawei.com" , Robert Richter , Jason Cooper , Arnd Bergmann , Marc Zyngier , "jcm@redhat.com" , Mark Brown , Bjorn Helgaas , "linux-arm-kernel@lists.infradead.org" , Matt Fleming , Ashwin Chaugule , Randy Dunlap , "Rafael J. Wysocki" , "linux-kernel@vger.kernel.org" , "suravee.suthikulpanit@amd.com" , Sudeep Holla , Olof Johansson Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3086 Lines: 79 On 7 February 2015 at 03:36, Hanjun Guo wrote: > On 2015年02月06日 18:34, G Gregory wrote: > [...] > >>>>>> >>>>>> -------------------------------------------------------------------------------- >>>>>> linux,uefi-stub-kern-ver | string | Copy of linux_banner from >>>>>> build. >>>>>> >>>>>> -------------------------------------------------------------------------------- >>>>>> +linux,uefi-stub-generated-dtb | bool | Indication for no DTB >>>>>> provided by >>>>>> + | | firmware. >>>>>> >>>>>> +-------------------------------------------------------------------------------- >>>>> >>>>> >>>>> Apologies for the late bikeshedding, but the discussion on this topic >>>>> previsously was lively enough that I thought I'd let it die down a bit >>>>> before seeing if I had anything to add. >>>>> >>>>> That, and I just realised something: >>>>> One alternative to this added DT entry is that we could treat the >>>>> absence of a registered UEFI configuration table as the indication >>>>> that no HW description was provided from firmware, since the stub does >>>>> not call InstallConfigurationTable() on the DT it generates. This does >>>>> move the ability to detect to after efi_init(), but this should be >>>>> fine for ACPI-purposes. >>>>> >>>> That would not work as expected in the kexec/Xen use case though as they >>>> may genuinely boot with DT from an ACPI host without UEFI. >>> >>> >>> I'm a little concerned by this case. How do we intend to pass stuff from >>> Xen to the kernel in this case? When we initially discussed the stub >>> prior to merging, we weren't quite sure if ACPI without UEFI was >>> entirely safe. >>> >>> The linux,uefi-stub-kern-ver property was originally intended as a >>> sanity-check feature to ensure nothing (including Xen) masqueraded as >>> the stub, but for some reason the actual sanity check was never >>> implemented. >>> >>>>> If that is deemed undesirable, I would still prefer Catalin's >>>>> suggested name ("linux,bare-dtb"), which describes the state rather >>>>> than the route we took to get there. >>>>> >>>> I agree. >>> >>> >>> I guess this would be ok, though it would be nice to know which agent >>> generated the DTB. >>> >> >> The most obvious scheme then is >> >> linux,bare-dtb = "uefi-stub"; >> >> otherwise we generate a new binding for every component in the boot path. > > > Leif, Mark, any comments on this? > As far as I remember, we did not finalize the decision to go with a stub generated property instead of some other means to infer that the device tree is not suitable for booting and ACPI should be preferred. We will be discussing the 'stub<->kernel interface as a boot protocol' topic this week at Connect, so let's discuss it in that context before signing off on patches like these. -- Ard. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/