Re: [PATCH v4 0/6] riscv: implement Ssqosid extension and CBQRI controllers

[Drew Fustini <fustini@kernel.org>]

On Wed, Jan 07, 2026 at 03:38:34PM +0800, yunhui cui wrote:
> Hi Drew,
> 
> On Tue, Jan 6, 2026 at 5:55 AM Drew Fustini <fustini@kernel.org> wrote:
> >
> > This series implements the RISC-V Quality-of-Service Identifiers
> > (Ssqosid) extension [1] which adds the srmcfg register. It also
> > implements the RISC-V Capacity and Bandwidth Controller QoS Register
> > Interface (CBQRI) specification [2]. Quality of Service (QoS) in this
> > context is concerned with shared resources on an SoC such as cache
> > capacity and memory bandwidth.
> >
> > Sssqosid srmcfg CSR
> > -------------------
> > The srmcfg CSR configures a hart with two identifiers:
> >
> >  - Resource Control ID (RCID)
> >  - Monitoring Counter ID (MCID)
> >
> > These identifiers accompany each request issued by the hart to shared
> > resource controllers. This allows the capacity and bandwidth resources
> > used by a software workload (e.g. a process or a set of processes) to be
> > controlled and monitored.
> 
> 1. The CBQRI specification does not mandate 64-byte access width for
> its registers. Therefore, is it necessary to add a field in the ACPI
> RQSC table?

Sorry, I don't follow. Why would a new field be needed in RQSC?

> 2. In addition, although CBQRI does not require configuring a specific
> number of RMIDs for each CLOSID like MPAM does, creating a control
> group will by default create a monitoring group. So on RISC-V, the
> number of MCIDs should be at least no less than that of RCIDs, right?

Yes, I have working on the assumption that the number of MCIDs (RMIDs)
will be greater than, or equal to, the number of RCIDs (e.g. CLOSIDs).

Chapter 6 of the CBQRI spec states that: "In a typical implementation,
the number of RCID bits implemented (for example, to support 10s of
RCIDs) might be smaller than the number of MCID bits implemented (for
example, to support 100s of MCIDs)."

I would be very interested if anyone can share the RCID and MCID count
for their CBQRI hardware implementation.

> 3. By the way, for Linux, could you also release a version of the
> CBQRI/Ssqosid patchset with ACPI support?

The series I am about to post for Ssqosid+CBQRI [1] just contains a
device tree example, but I will do a followup series for RQSC. The
kernel branch [2] from the RQSC proof-of-concept was based on v6.14 so I
need to rebase it. The good thing is that 6.19 now has the PPTT helpers
from the MPAM driver series.

Thanks,
Drew

[1] https://github.com/tt-fustini/linux/tree/b4/ssqosid-cbqri
[2] https://github.com/tt-fustini/linux/tree/dfustini/cbqri-mpam-snapshot-v6.14-rc1