Re: [PATCH 00/11 v2] RISC-V: support CLIC v0.9 specification

[Alistair Francis <alistair23@gmail.com>]

On Tue, Aug 20, 2024 at 2:08 AM Ian Brockbank <Ian.Brockbank@cirrus.com> wrote:
>
> [Resubmission now the merge is correct]
>
> This patch set gives an implementation of "RISC-V Core-Local Interrupt
> Controller(CLIC) Version 0.9-draft-20210217". It comes from [1], where
> you can find the pdf format or the source code.

Thanks for the patches!

I left some comments on the cover letter and throughout the series.

The main points are that we need to support a release spec (draft is
ok, but it needs to be tagged as a version). On top of that we want to
try and keep the CSR changes in target/riscv. We don't want to be
including the hw/intc code all over the place. time_helper.c for
example is how the ACLINT works, where we try to keep as much of the
CPU code in target/riscv.

Also we will need extension checks for all of the relevant CLIC
extensions. Guest code should not notice any changes after this series
unless they enable the CLIC extensions.

Alistair

>
> This is based on the implementation from 2021 by Liu Zhiwei [3], who took
> over the job from Michael Clark, who gave the first implementation of
> clic-v0.7 specification [2]. I believe this implementation addresses all
> the comments in Liu Zhiwei's RFC patch thread.
>
> This implementation follows the CLIC 0.9-stable draft at 14 March 2024,
> with the following exceptions and implementation details:
>  - the CLIC control registers are memory-mapped as per earlier drafts (in
>    particular version 0.9-draft, 20 June 2023)
>  - the indirect CSR control in 0.9-stable is not implemented
>  - the vector table can be either handler addresses (as per the spec)
>    or a jump table where each entry is processed as an instruction,
>    selectable with version number v0.9-jmp
>  - each hart is assigned its own CLIC block
>  - if PRV_S and/or PRV_M are supported, they are currently assumed to follow
>    the PRV_M registers; a subsequent update will address this
>  - support for PRV_S and PRV_M is selectable at CLIC instantiation
>  - PRV_S and PRV_U registers are currently separate from PRV_M; a subsequent
>    update will turn them into filtered views onto the PRV_M registers
>  - each hart is assigned its own CLIC block
>  - support for PRV_S and PRV_M is selectable at CLIC instantiation by
>    passing in a base address for the given modes; a base address of 0 is
>    treated as not supported
>  - PRV_S and PRV_U registers are mapped  onto the PRV_M controls with
>    appropriate filtering for the access mode
>  - the RISCV virt machine has been updated to allow CLIC emulation by
>    passing "machine=virt,clic=on" on the command line; various other
>    parameters have been added to allow finer control of the CLIC behavior
>
> The implementation (in jump-table mode) has been verified to match the
> Cirrus Logic silicon (PRV_M only), which is based upon the Pulp
> implementation [4] as of June 2023.
>
> The implementation also includes a selection of qtests designed to verify
> operation in all possible combinations of PRV_M, PRV_S and PRV_U.
>
> [1] specification website: https://github.com/riscv/riscv-fast-interrupt.
> [2] Michael Clark origin work:
> https://github.com/sifive/riscv-qemu/tree/sifive-clic.
> [3] RFC Patch submission by Liu Zhiwei:
> https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg01417.html
> [4] Pulp implementation of CLIC: https://github.com/pulp-platform/clic
>
> Ian Brockbank (11):
>     target/riscv: Add CLIC CSR mintstatus
>     target/riscv: Update CSR xintthresh in CLIC mode
>     hw/intc: Add CLIC device
>     target/riscv: Update CSR xie in CLIC mode
>     target/riscv: Update CSR xip in CLIC mode
>     target/riscv: Update CSR xtvec in CLIC mode
>     target/riscv: Update CSR xnxti in CLIC mode
>     target/riscv: Update interrupt handling in CLIC mode
>     target/riscv: Update interrupt return in CLIC mode
>     hw/riscv: add CLIC into virt machine
>     tests: add riscv clic qtest case and a function in qtest
>
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>