From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: Design doc of adding ACPI support for arm64 on Xen - version 3 Date: Mon, 17 Aug 2015 23:43:02 -0700 Message-ID: <55D2D3F6.1030405@citrix.com> References: <55CE0247.4030805@linaro.org> <55D21AE2020000780009B6D4@prv-mh.provo.novell.com> <55D2099F.2000903@citrix.com> <55D2CC5F02000078000D6BC5@prv-mh.provo.novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55D2CC5F02000078000D6BC5@prv-mh.provo.novell.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Jan Beulich , shannon.zhao@linaro.org Cc: hangaohuai@huawei.com, ian.campbell@citrix.com, stefano.stabellini@eu.citrix.com, peter.huangpeng@huawei.com, andrew@fubar.geek.nz, stefano.stabellini@citrix.com, david.vrabel@citrix.com, zhaoshenglong@huawei.com, boris.ostrovsky@oracle.com, xen-devel@lists.xen.org, parth.dixit@linaro.org, christoffer.dall@linaro.org List-Id: xen-devel@lists.xenproject.org Hi Jan, On 17/08/2015 22:10, Jan Beulich wrote: >>>> Julien Grall 08/17/15 6:27 PM >>> >> On 17/08/2015 08:33, Jan Beulich wrote: >>>>>> On 14.08.15 at 16:59, wrote: >>>> b) Create EFI_MEMORY_DESCRIPTOR table. This will add memory start and >>>> size information of Dom0. And Dom0 will get the memory information >>>> through this EFI table. >>> >>> To some degree the same applies here: While I see that you have no >>> legacy vehicle like x86's E820, I also don't see how Dom0 - not being >>> able to make EFI boot or runtime services calls - would get hold of this >>> table. And if a non-EFI mechanism is to be used here, using the EFI >>> data structure would turn out to be just an arbitrary (or convenience) >>> decision, not something inherently required. Which I think should be >>> said explicitly if so, rather than leaving the reader guess. >> >> It's not an arbitrary decision, when UEFI stub in Linux is using device >> tree properties to pass the UEFI table to the kernel ([1]). >> >> When booting on Xen with ACPI, dom0 will use the non-EFI entry point. >> The easiest way to pass the memory information to Linux is using the >> UEFI DT properties. > > In which case it is even more arbitrary to use the EFI data structure to > convey memory information (instead of expressing it in plain DT, which is > how I blindly assume non-EFI does it). Of course there's the small chance > that "UEFI DT properties" implies a certain binary format, but it's still odd > for a non-EFI entry point to assume EFI properties to be there... Linux is able to boot either on ACPI or DT. When ACPI is used, the EFI stub (mandatory) will create a small DT in order to pass the command line and other informations (such as the EFI memory table) to the kernel. This is because the stub is self-contained and and never use variable living in the kernel. In order to know whether you are booting using DT or ACPI, they check if the DT contains only the /chosen node. Actually the EFI-stub will always jumped on the non-EFI path. By passing the minimal DT as suggested on the design doc, we are avoiding to get a different code path for Xen in the kernel and we are finally acting as the EFI-stub was a nop for DOM0. So I don't see how this would be arbitrary... Regards, -- Julien Grall