[PATCH v2 0/5] Add support for RPMI to U-Boot

[Michal Simek]

On 7/9/26 16:54, Charles Perry wrote:
> On Thu, Jul 09, 2026 at 03:02:11PM +0200, Michal Simek wrote:
>>
>>
>> On 7/8/26 23:51, Charles Perry wrote:
>>> Hello,
>>>
>>> This series adds support for RISC-V Platform Management Interface (RPMI) to
>>> U-Boot. RPMI is an OS-agnostic protocol for communication between an
>>> Application Processor (AP) and a Platform Microcontroller (PuC) [1]. The
>>> goals and purpose of RPMI are similar to ARM's SCMI.
>>
>>  From the first look it looks like SCMI. Why do you introducing something
>> what can be replaced by SCMI?
>> And SCMI has only specific ARM transport layer but the rest is arch independent.
> 
> Yes, there are alot of similarities between RPMI and SCMI. I found some
> justification for this in some Linux Plumbers slide deck on RISC-V power
> management by Paul Walmsley [1]:
> 
>   * The hardware is more sophisticated
>   * The software is more sophisticated
>   * Some stakeholders haven’t had input in the past
>   * RISC-V “big tent” philosophy
> 
> I think this is referring to the SBI spec of RISC-V vs arm's PSCI but the
> same arguments may as well apply to RPMI vs SCMI.
> 
> Some other arguments:
> 
>   * The microcontroller side is made easier with RPMI because of librpmi [2].
>     SCMI has SCP-firmware [3] which is a quite complex project compared to
>     librpmi. Also SCP-firmware doesn't accept contribution anymore.
>   * RPMI is already in Linux.
> 
> For what I'm doing, RPMI is what gave me the first results (controlling
> clocks) the quickest because all the pieces were present in Linux, OpenSBI
> and librpmi. There are however lots of missing service drivers in Linux and
> some other important OS like u-boot don't have support for RPMI at all. So
> even though I gave you a bunch of reason for saying yes to RPMI, I do have
> some doubt about how long it will take to bring RPMI on par with SCMI,
> making the SCMI-for-RISCV transport that you suggest more appealing.
> 
> [1]: https://lpc.events/event/2/contributions/197/attachments/133/165/RISC-V_Platform_Power_Management.pdf (slide 22)
> [2]: https://github.com/riscv-software-src/librpmi
> [3]: https://gitlab.arm.com/firmware/SCP-firmware
> 
>>
>> In our case where we have Microblaze V in programmable logic I can't see any
>> reason to use RPMI for talking to the same server if I need to do it from
>> ARM side too via SCMI.
>>
>> I pretty much think that there should be communication with ARM and instead
>> of creating another firmware interface talk to each other and have only one
>> which can be used across multiple architectures.

I have sent RFC patch to eliminate ARM from SCMI here

https://lore.kernel.org/all/d7f7e8c9589d937b60e43168845ab4fda15037a3.1783603600.git.michal.simek@amd.com/

and feedback is quite positive. I think it is more or less question to Microchip 
if you want to take responsibility on another firmware interface (I understand 
that it is approved, etc) or just use what it is around for longer time.

Thanks,
Michal