linux-kernel - Re: [PATCH 7/8] riscv: Use pgtable_l4_enabled to output mmu type in cpuinfo

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Message-ID: <CAAhSdy3JU8ae8Gx-4iNiOKbC027-Cgjc_8=BYEp1sO3pW6D5XA@mail.gmail.com>
Date:   Mon, 25 May 2020 11:51:31 +0530
From:   Anup Patel <anup@...infault.org>
To:     Alexandre Ghiti <alex@...ti.fr>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Zong Li <zong.li@...ive.com>, Christoph Hellwig <hch@....de>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH 7/8] riscv: Use pgtable_l4_enabled to output mmu type in cpuinfo

On Sun, May 24, 2020 at 2:47 PM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> Now that the mmu type is determined at runtime using SATP
> characteristic, use the global variable pgtable_l4_enabled to output
> mmu type of the processor through /proc/cpuinfo instead of relying on
> device tree infos.
>
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> Reviewed-by: Anup Patel <anup@...infault.org>
> Reviewed-by: Palmer Dabbelt <palmerdabbelt@...gle.com>
> ---
>  arch/riscv/boot/dts/sifive/fu540-c000.dtsi |  4 ----
>  arch/riscv/kernel/cpu.c                    | 24 ++++++++++++----------
>  2 files changed, 13 insertions(+), 15 deletions(-)
>
> diff --git a/arch/riscv/boot/dts/sifive/fu540-c000.dtsi b/arch/riscv/boot/dts/sifive/fu540-c000.dtsi
> index 7db861053483..6138590a2229 100644
> --- a/arch/riscv/boot/dts/sifive/fu540-c000.dtsi
> +++ b/arch/riscv/boot/dts/sifive/fu540-c000.dtsi
> @@ -50,7 +50,6 @@
>                         i-cache-size = <32768>;
>                         i-tlb-sets = <1>;
>                         i-tlb-size = <32>;
> -                       mmu-type = "riscv,sv39";
>                         reg = <1>;
>                         riscv,isa = "rv64imafdc";
>                         tlb-split;
> @@ -74,7 +73,6 @@
>                         i-cache-size = <32768>;
>                         i-tlb-sets = <1>;
>                         i-tlb-size = <32>;
> -                       mmu-type = "riscv,sv39";
>                         reg = <2>;
>                         riscv,isa = "rv64imafdc";
>                         tlb-split;
> @@ -98,7 +96,6 @@
>                         i-cache-size = <32768>;
>                         i-tlb-sets = <1>;
>                         i-tlb-size = <32>;
> -                       mmu-type = "riscv,sv39";
>                         reg = <3>;
>                         riscv,isa = "rv64imafdc";
>                         tlb-split;
> @@ -122,7 +119,6 @@
>                         i-cache-size = <32768>;
>                         i-tlb-sets = <1>;
>                         i-tlb-size = <32>;
> -                       mmu-type = "riscv,sv39";
>                         reg = <4>;
>                         riscv,isa = "rv64imafdc";
>                         tlb-split;

Your PATCH6 is already doing the right thing by skipping CPU DT
nodes that don't have "mmu-type" DT property.

The "mmu-type" DT property is very critical for RUNTIME M-mode
firmware (OpenSBI) because it tells whether a given CPU has MMU
(or not). This is also in agreement with the current DT bindings
document for RISC-V CPUs.

I suggest to drop the change in sifive/fu540-c000.dtsi and rest of
the patch is fine so my Reviewed-by still holds.

Regards,
Anup

> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
> index 40a3c442ac5f..38a699b997a8 100644
> --- a/arch/riscv/kernel/cpu.c
> +++ b/arch/riscv/kernel/cpu.c
> @@ -8,6 +8,8 @@
>  #include <linux/of.h>
>  #include <asm/smp.h>
>
> +extern bool pgtable_l4_enabled;
> +
>  /*
>   * Returns the hart ID of the given device tree node, or -ENODEV if the node
>   * isn't an enabled and valid RISC-V hart node.
> @@ -54,18 +56,19 @@ static void print_isa(struct seq_file *f, const char *isa)
>         seq_puts(f, "\n");
>  }
>
> -static void print_mmu(struct seq_file *f, const char *mmu_type)
> +static void print_mmu(struct seq_file *f)
>  {
> +       char sv_type[16];
> +
>  #if defined(CONFIG_32BIT)
> -       if (strcmp(mmu_type, "riscv,sv32") != 0)
> -               return;
> +       strncpy(sv_type, "sv32", 5);
>  #elif defined(CONFIG_64BIT)
> -       if (strcmp(mmu_type, "riscv,sv39") != 0 &&
> -           strcmp(mmu_type, "riscv,sv48") != 0)
> -               return;
> +       if (pgtable_l4_enabled)
> +               strncpy(sv_type, "sv48", 5);
> +       else
> +               strncpy(sv_type, "sv39", 5);
>  #endif
> -
> -       seq_printf(f, "mmu\t\t: %s\n", mmu_type+6);
> +       seq_printf(f, "mmu\t\t: %s\n", sv_type);
>  }
>
>  static void *c_start(struct seq_file *m, loff_t *pos)
> @@ -90,14 +93,13 @@ static int c_show(struct seq_file *m, void *v)
>  {
>         unsigned long cpu_id = (unsigned long)v - 1;
>         struct device_node *node = of_get_cpu_node(cpu_id, NULL);
> -       const char *compat, *isa, *mmu;
> +       const char *compat, *isa;
>
>         seq_printf(m, "processor\t: %lu\n", cpu_id);
>         seq_printf(m, "hart\t\t: %lu\n", cpuid_to_hartid_map(cpu_id));
>         if (!of_property_read_string(node, "riscv,isa", &isa))
>                 print_isa(m, isa);
> -       if (!of_property_read_string(node, "mmu-type", &mmu))
> -               print_mmu(m, mmu);
> +       print_mmu(m);
>         if (!of_property_read_string(node, "compatible", &compat)
>             && strcmp(compat, "riscv"))
>                 seq_printf(m, "uarch\t\t: %s\n", compat);
> --
> 2.20.1
>