Re: Adding RISC-V to EBBR

On 8/20/20 10:09 PM, Atish Patra wrote:

On Thu, Aug 20, 2020 at 1:03 PM Heinrich Schuchardt xypron.glpk@gmx.de wrote:

...

On 8/20/20 9:32 PM, Atish Patra wrote:

...

+Paul

On Thu, Aug 20, 2020 at 8:46 AM Grant Likely <grant.likely@arm.com mailto:grant.likely@arm.com> wrote:

Hi Atish,

I'm happy to add RISC-V content to EBBR. EBBR was originated as a
community driven document, and though it was created to solve problems
in the Arm ecosystem, it is not limited to Arm platforms.

g.

On 20/08/2020 01:03, Atish Patra wrote:
> Hi All,
> We are interested in adopting EBBR as the boot specification for the
> embedded RISC-V platforms.
> We firmly believe that EBBR is a very well defined specification for
> boot requirement and there
> is no need for reinventing the wheel for RISC-V. Hence, this is a
> thread to discuss all the requirements
> for adding RISC-V to EBBR.  Here is my current understanding. Please
> correct me if I am wrong.
>
> Logistic Requirement:
> 1. As per the contribution guidelines[1], patches should be sent to
> boot-architecture@lists.linaro.org
<mailto:boot-architecture@lists.linaro.org>.
>      and the specification will be hosted under "ARM-software" Github.
> I am hoping that introducing RISC-V
>      related changes are okay with the current maintainers.

Yes, I will accept RISC-V content

> 2. The specification is licensed under Creative Commons. The RISC-V
> related changes will refer to
>      some of the RISC-V specifications as well. AFAIK, there shouldn't
> be an issue with that.

Yes

> 3. It should be okay to add other copyrights in addition to "Arm
> Limited and Contributors".

That statement reflects the origin of the document, and I haven't
changed it because I did want a long list of copyright holders on the
front page. Go ahead and propose changes to the formatting.

> Technical Requirement:
> 1. Software status:
>      a. UEFI support for RISC-V Linux kernel is already available in
> the mailing list[2]. The targeted upstream
>      merge is the 5.10 merge window.
>      b. U-Boot already supports UEFI for RISC-V.
>      c. EDK2 upstreaming is currently under progress [3] as well.
>
>    Is it okay to start sending patches for EBBR RISC-V related changes
> now or do we need to wait for EDK2 and Linux
>    kernel patches to be available upstream ?

Landing features in mainline U-Boot/Linux/EDK2/etc. is not required, but
the general guidance on EBBR is to only require features that are
achievable. If any feature isn't feasible in the near future, then I'd
caution against adding it to EBBR.

Got it. Thanks for the clarification.

> 2. RISC-V related sections in EBBR
>      a. UEFI:
>          Currently, RISC-V doesn't support a  EFI_RESET_SYSTEM boot
> service as firmware doesn't have a standard way
>          to reset the system. There is a proposal to add a system
reset
> function to Supervisor Binary Specification(SBI) which
>          can be mapped to EFI_RESET_SYSTEM by the firmware. Apart from
> that, I believe RISC-V supports all UEFI boot and
>          run time services mandated by EBBR. Is it a blocker for
RISC-V
> EBBR compatibility?

Reset system if a fundamental interface. I'm not keen to relax this
requirement.

As per the specification, Reset system is only mandatory for boot services. But I couldn't find anything in the EFI stub in the kernel that actually invokes it. I see only watchdog in U-boot using it to comply with the watchdog requirement of UEFI spec. I am not sure if EDK2 has other usages. Is it supposed to be used by the firmware/boot loader only ?

Usages of the service can be found in:

• GRUB (command reboot)
• iPXE (commands reboot, poweroff)
• EFI shell (command reset)

Linux uses it in

• arch/x86/kernel/reboot.c
• arch/arm64/kernel/process.c

via function efi_reboot() implemented in drivers/firmware/efi/reboot.c.

As per my understanding, efi_reboot uses the runtime efi service that gets called after ExitBootService(). This is marked optional in the EBBR spec. I was talking about the reset_system user as a boot service.

As per EBBR spec, "ResetSystem() is required to be implemented in boot services, but it is optional for runtime services"

Yes, only GRUB, iPXE, and EFI shell are usages before ExitBootServices().

If you want an operating system example of usage before ExitBootServices():

OpenBSD has a boot prompt that is executed before ExitBootServices() and offers commands 'reboot' and 'poweroff' via UEFI's ResetSystem().

Best regards

Heinrich