From mboxrd@z Thu Jan 1 00:00:00 1970 From: Parth Dixit Subject: Re: [PATCH v7 04/17] ARM64 / ACPI: Introduce early_param for "acpi" and pass acpi=force to enable ACPI Date: Wed, 21 Jan 2015 22:21:16 +0530 Message-ID: References: <20150119151350.21B65C40948@trevor.secretlab.ca> <54BD3803.6020307@redhat.com> <20150119175233.GK11835@e104818-lin.cambridge.arm.com> <20150119180122.GJ21553@leverpostej> <54BE1FEA.5040109@linaro.org> <20150121152326.GD6358@e104818-lin.cambridge.arm.com> <54BFC5F0.3020500@redhat.com> <20150121154243.GE6358@e104818-lin.cambridge.arm.com> <54BFCE4D.2060806@redhat.com> <20150121161652.GH6358@e104818-lin.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Return-path: Received: from mail-wi0-f174.google.com ([209.85.212.174]:51125 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751934AbbAUQvS (ORCPT ); Wed, 21 Jan 2015 11:51:18 -0500 Received: by mail-wi0-f174.google.com with SMTP id n3so15466858wiv.1 for ; Wed, 21 Jan 2015 08:51:17 -0800 (PST) In-Reply-To: <20150121161652.GH6358@e104818-lin.cambridge.arm.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Catalin Marinas Cc: Jon Masters , Stefano Stabellini , "hanjun.guo@linaro.org" , Mark Rutland , "grant.likely@linaro.org" , Ard Biesheuvel , "linaro-acpi@lists.linaro.org" , Will Deacon , "wangyijing@huawei.com" , Rob Herring , Lorenzo Pieralisi , Al Stone , Timur Tabi , "linux-acpi@vger.kernel.org" , Charles Garcia-Tobin , "phoenix.liyi@huawei.com" , Robert Richter , Jason Cooper , Arnd Bergmann , Marc Zyngier On 21 January 2015 at 21:46, Catalin Marinas wrote: > On Wed, Jan 21, 2015 at 04:05:33PM +0000, Jon Masters wrote: >> On 01/21/2015 10:42 AM, Catalin Marinas wrote: >> > On Wed, Jan 21, 2015 at 03:29:52PM +0000, Jon Masters wrote: >> >> On 01/21/2015 10:23 AM, Catalin Marinas wrote: >> >>> I have some questions for the ACPI and EFI folk: >> >>> >> >>> 1. When booting with ACPI, are the EFI run-time services required for >> >>> anything? If yes, Xen may have a bigger problem >> >> >> >> Yes. At least for some things. For example, installing an Operating >> >> System would require that you make runtime services calls to set the >> >> BootOrder/BootNext variables, and so on. Further, we use the GetTime >> >> service and EFI based reboot to avoid having special drivers. I had >> >> those added to SBBR as requirements for that reason. >> > >> > So what would a kexec'ed kernel do here? Or we usually expect it to be >> > short lived and doesn't need reboot, nor GetTime. >> >> In the use case that I have, it'll use EFI Runtime Servies to handle >> both the time of day (which it will need) and to subsequently reboot. >> This is currently being worked on (integration into kdump). > > So the EFI run-time services (and EFI tables) will be preserved across > kexec? Could Xen not to something similar? > >> >>> 2. Could a boot loader (either kernel doing kexec or Xen) emulate the >> >>> EFI system/config tables and still make them useful to the kernel but >> >>> without EFI_BOOT or EFI_RUNTIME_SERVICES? >> >> >> >> Yes. But again, without the other required pieces (including the >> >> services function pointers in the systab which are required) you'd crash >> >> soon after boot trying to make those calls. >> > >> > My point was whether you can still pass information like RSDP address >> > via EFI tables but explicitly disable runtime services so that the >> > kernel won't try to make such calls (and crash). >> >> Yes. As Graeme says, it works just to pass in the ACPI information and >> turn off EFI *BUT* it does not work to say you have EFI and then not >> provide the correct EFI services. To do so is out of spec, and in fact >> it's one reason we weren't able to turn the GetTime service on generally >> for x86 - some older x86 boxes didn't implement it originally (another >> reason on our end we're requiring all of these services on day one so >> that there won't be time for someone to miss them in firmware). This is the use case i am talking about, we have a wroking setup with efi disabled and rsdp passed via dtb, right now its done by adding a "rsdp" field in the chosen node. Do we have a formal way to pass RSDP without EFI? if not, it would be good to have dtb binding which we can use to pass RSDP address to kernel for ACPI. > OK, thanks for confirming this. So the answer to my second question is > "not really". > > -- > Catalin