linux-kernel - Re: [PATCH v2 0/5] Dedicated CLINT timer driver

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Message-ID: <mhng-4d70be69-ef20-4d38-bda4-ec4101530c0a@palmerdabbelt-glaptop1>
Date:   Mon, 13 Jul 2020 16:02:01 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Anup Patel <Anup.Patel@....com>
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        robh+dt@...nel.org, daniel.lezcano@...aro.org, tglx@...utronix.de,
        Damien Le Moal <Damien.LeMoal@....com>,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        anup@...infault.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Anup Patel <Anup.Patel@....com>
Subject:     Re: [PATCH v2 0/5] Dedicated CLINT timer driver

On Sat, 27 Jun 2020 09:19:52 PDT (-0700), Anup Patel wrote:
> The current RISC-V timer driver is convoluted and implements two
> distinct timers:
>  1. S-mode timer: This is for Linux RISC-V S-mode with MMU. The
>     clocksource is implemented using TIME CSR and clockevent device
>     is implemented using SBI Timer calls.
>  2. M-mode timer: This is for Linux RISC-V M-mode without MMU. The
>     clocksource is implemented using CLINT MMIO time register and
>     clockevent device is implemented using CLINT MMIO timecmp registers.
>
> This patchset removes clint related code from RISC-V timer driver and
> arch/riscv directory. Instead, the series adds a dedicated MMIO based
> CLINT driver under drivers/clocksource directory which can be used by
> Linux RISC-V M-mode (i.e NoMMU Linux RISC-V).
>
> The patchset is based up Linux-5.8-rc2 and can be found at riscv_clint_v2
> branch of: https://github.com/avpatel/linux.git
>
> This series is tested on:
>  1. QEMU RV64 virt machine using Linux RISC-V S-mode
>  2. QEMU RV32 virt machine using Linux RISC-V S-mode
>  3. QEMU RV64 virt machine using Linux RISC-V M-mode (i.e. NoMMU)
>
> Changes since v1:
>  - Rebased series on Linux-5.8-rc2
>  - Added pr_warn() for case where ipi_ops not available in PATCH1
>  - Updated ipi_inject() prototype to use "struct cpumask *" in PATCH1
>  - Updated CLINT_TIMER kconfig option to depend on RISCV_M_MODE in PATCH4
>  - Added riscv,clint0 compatible string in DT bindings document
>
> Anup Patel (5):
>   RISC-V: Add mechanism to provide custom IPI operations
>   RISC-V: Remove CLINT related code
>   clocksource/drivers/timer-riscv: Remove MMIO related stuff
>   clocksource/drivers: Add CLINT timer driver
>   dt-bindings: timer: Add CLINT bindings

This all generally LGTM, though I haven't been through the code line-by-line
yet.  It touches a bunch of trees, so I'd prefer to have some Acks before
merging -- I'll dig through the RISC-V specific stuff, but the new CLINT driver
probhably deserves a look from one of the clocksource folks.

I think the only issue is that the port will be broken between patch 2 and 4,
as at that point we won't have an M-mode timer driver.  I think it shouldn't be
too much to just reorder these, LMK if you want to do it or you want me to.

Thanks!

>
>  .../bindings/timer/sifive,clint.txt           |  34 +++
>  arch/riscv/Kconfig                            |   2 +-
>  arch/riscv/include/asm/clint.h                |  39 ---
>  arch/riscv/include/asm/smp.h                  |  11 +
>  arch/riscv/include/asm/timex.h                |  28 +--
>  arch/riscv/kernel/Makefile                    |   2 +-
>  arch/riscv/kernel/clint.c                     |  44 ----
>  arch/riscv/kernel/sbi.c                       |  14 ++
>  arch/riscv/kernel/setup.c                     |   2 -
>  arch/riscv/kernel/smp.c                       |  44 ++--
>  arch/riscv/kernel/smpboot.c                   |   4 +-
>  drivers/clocksource/Kconfig                   |  12 +-
>  drivers/clocksource/Makefile                  |   1 +
>  drivers/clocksource/timer-clint.c             | 229 ++++++++++++++++++
>  drivers/clocksource/timer-riscv.c             |  17 +-
>  include/linux/cpuhotplug.h                    |   1 +
>  16 files changed, 337 insertions(+), 147 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/timer/sifive,clint.txt
>  delete mode 100644 arch/riscv/include/asm/clint.h
>  delete mode 100644 arch/riscv/kernel/clint.c
>  create mode 100644 drivers/clocksource/timer-clint.c