[RFC PATCH 0/1] Add boot hartid to a Device tree

Atish Patra atishp at atishpatra.org
Fri Mar 6 01:34:18 CET 2020

On Wed, Mar 4, 2020 at 7:22 PM Schaefer, Daniel (DualStudy)
<daniel.schaefer at hpe.com> wrote:
> Hi,
> I have started to implement the corresponding changes in EDK2: https://github.com/changab/edk2-staging-riscv/compare/5f63e9249751ccb9302514455b9a1a7038f34547...RISC-V-DT-fixup
> What happens is: The DTB is embedded in the FW image and passed to sbi_init in SEC phase. We initialize OpenSBI as early as possible and because it also wants to modify the device tree, I have to pass it the DTB as next_arg1.
> Then it's passed to PEI in the firmware context and further to DXE via a HOB. In DXE the boot-hartid is inserted and it's installed into the EFI system config table from where the EFISTUB reads it.
> Unfortunately I don't get any console output after the EFISTUB calls ExitBootServices, so my patch is still WIP.
> Atish, which platform file in OpenSBI did you use to test your changes? platform/qemu/virt/platform.c or platform/sifive/fu540/platform.c ?

Both. I have verified bootefi boot on Qemu and Unleashed.

> Maybe the failure is unrelated to the new patches - we've never booted Linux from EDKII yet.

I have never tried EDKII patches as well. I will give it a try. You
can add a quick hack can be added in OpenSBI to add the chosen node
By doing that, you ensure that EDK2 is unchanged and try my EFI stub
patches. I might have missed something in EFI stub as well :).

> I'm a bit skeptical whether DT is the best way to pass the boothartid to the kernel. Ard has argued that it's good because it's independent from UEFI, but the proper kernel doesn't read the hartid from there - it gets it from a0. Only the EFISTUB reads the hartid from the device tree. Therefore the solution we need is EFI specific anyways, right?


> One of the design goals is that we don't want to force bootloaders, which load the EFISTUB (e.g. UEFI Shell, grub chainloading, systemd-boot), to change.

I don't know how systemd-boot works but grub doesn't need to modify
DT. The stage loading the grub must have already made that

> If we let the firmware embed the hartid in the DT, the user cannot swap out the DT later for their custom one. They need to use the one given by the firmware.
> Of course we could add commands and config to bootloaders to load and fixup (embed hartid) the device tree... but, as mentioned earlier, we want to avoid that.
> Additionally from EDKII side we're also planning to run later stages, including the bootloader, in S-Mode, where they wouldn't even have access to mhartid and thus couldn't fixup the DT.
> If instead the firmware writes the hartid into the EFI system config table, the EFISTUB can read it from there, just like it does the device tree already. Then bootloaders can put a user supplied DT in the config table, too, like they always have.
> What do you all think - does that make sense?
> - Daniel
> On 2/25/20 10:07 AM, Ard Biesheuvel wrote:
> On Tue, 25 Feb 2020 at 09:59, Chang, Abner (HPS SW/FW Technologist)
> <abner.chang at hpe.com> wrote:
> -----Original Message-----
> From: Ard Biesheuvel [mailto:ard.biesheuvel at linaro.org]
> Sent: Tuesday, February 25, 2020 4:48 PM
> To: Chang, Abner (HPS SW/FW Technologist) <abner.chang at hpe.com>
> Cc: Atish Patra <atishp at atishpatra.org>; Heinrich Schuchardt
> <xypron.glpk at gmx.de>; Atish Patra <atish.patra at wdc.com>; U-Boot Mailing
> List <u-boot at lists.denx.de>; Alexander Graf <agraf at csgraf.de>; Anup Patel
> <anup.patel at wdc.com>; Bin Meng <bmeng.cn at gmail.com>; Joe
> Hershberger <joe.hershberger at ni.com>; Loic Pallardy
> <loic.pallardy at st.com>; Lukas Auer <lukas.auer at aisec.fraunhofer.de>;
> Marek Behún <marek.behun at nic.cz>; Marek Vasut
> <marek.vasut at gmail.com>; Patrick Delaunay <patrick.delaunay at st.com>;
> Peng Fan <peng.fan at nxp.com>; Philippe Reynes
> <philippe.reynes at softathome.com>; Simon Glass <sjg at chromium.org>;
> Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>; Stefano Babic
> <sbabic at denx.de>; Thierry Reding <treding at nvidia.com>; Tom Rini
> <trini at konsulko.com>; leif at nuviainc.com; Schaefer, Daniel (DualStudy)
> <daniel.schaefer at hpe.com>
> Subject: Re: [RFC PATCH 0/1] Add boot hartid to a Device tree
> On Tue, 25 Feb 2020 at 09:28, Chang, Abner (HPS SW/FW Technologist)
> <abner.chang at hpe.com> wrote:
> -----Original Message-----
> From: Atish Patra [mailto:atishp at atishpatra.org]
> <snip header soup>
> On Mon, Feb 24, 2020 at 3:35 PM Ard Biesheuvel
> <ard.biesheuvel at linaro.org> wrote:
> On Tue, 25 Feb 2020 at 00:22, Heinrich Schuchardt
> <xypron.glpk at gmx.de>
> wrote:
> On 2/24/20 11:19 PM, Atish Patra wrote:
> The RISC-V booting protocol requires the hart id to be present in
> "a0"
> register. This is not a problem for bootm/booti commands as
> they directly jump to Linux kernel. However, bootefi jumps to
> a EFI boot stub code in Linux kernel which acts a loader and
> jumps to real Linux after terminating the boot services. This
> boot stub code has to be aware of the boot hart id so that it
> can set it in "a0" before jumping to Linux kernel. Currently,
> UEFI protocol doesn't have any mechanism to pass the boot hart
> id to an EFI executable. We should keep it this way as this is
> a RISC-V specific requirement rather than a UEFI requirement.
> Out of the all
> possible options, device tree seemed to be the best choice to do this job.
> The detailed discussion can be found in the following thread.
> abs.org_patch_1233664_&d=DwIBaQ&c=C5b8zRQO1miGmBeVZ2LFWg&r=_S
> N4Vgi4Ulkskz6qU3NYRO03nHp9P7Z5q59A3E&m=J8GY_HS3fV_cJH9duXP739y
> 0hDK
> 3qfHGNx2Dpcf-UBY&s=iVpRlpTOME_A-
> O5STNbXXawkW24gxy2yi56Q8AtZ2bI&e=
> The above mentioned patch is obsoleted by the new suggestion.
> Thanks for pointing that out to avoid confusion.
> This patch updates the device tree in arch_fixup_fdt() which
> is common for all booting commands. As a result, the DT
> modification doesn't require any efi related arch specific
> functions and all DT related modifications are contained at
> one place. However, the hart id node will be available for
> Linux even if the kernel is booted using
> bootm command.
> If that is not acceptable, we can always move the code to an
> efi specific function.
> Does a related Linux patch already exist?
> Yes. But in my local tree ;). It will be included in RISC-V EFI stub
> support series which I am planning to post in a couple of days.
> How about EDK2?
> RISC-V is not supported at all yet in EDK2.
> The EDK2 patches are out there and reviewed. I guess it will be
> available in mainline EDK2 pretty soon.
> Yes, currently we are working on edk2 CI testing for RISCV64 arch.  We
> hope edk2 RISC-V port could be in mainstream in Mar.
> Excellent! Is this core support? Or do you have a platform implemented as
> well that can be upstreamed?
> Yes we do have platform implementations to be upstreamed, below is the latest status of RISC-V edk2 port. We will have to update status later because we just merged OpenSBI tag 0.6 to edk2 RISC-V.
> https://github.com/riscv/riscv-uefi-edk2-docs
> Good to know! I saw some patches going by on the mailing list, but it
> is hard to derive the current state of affairs from that.
> I'm glad to see you did not make the same mistake we made on ARM and
> omit the PEI phase entirely.
> What I did notice is the use of APRIORI PEI and APRIORI DXE sections
> in your platform descriptions. I recommend you try to avoid that, as
> it is a maintenance burden going forward: instead, please use dummy
> protocols and NULL library class resolutions if you need to make
> generic components depend on platform specific protocols. Also, please
> document this - the APRIORI section does not explain *why* you have to
> circumvent the ordinary dependency tree based module dispatch.


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