linux-kernel - Re: [PATCH 5/5] riscv/efi_stub: Support for 64bit boot-hartid

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Message-ID: <CAMj1kXFhEBv7MVCKZuXdx9=hZx3qWbkATdLDwXAe_Zn9Xyx=dg@mail.gmail.com>
Date:   Wed, 25 May 2022 17:48:58 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Sunil V L <sunilvl@...tanamicro.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Atish Patra <atishp@...osinc.com>,
        Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
        Anup Patel <apatel@...tanamicro.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Sunil V L <sunil.vl@...il.com>
Subject: Re: [PATCH 5/5] riscv/efi_stub: Support for 64bit boot-hartid

On Wed, 25 May 2022 at 17:11, Sunil V L <sunilvl@...tanamicro.com> wrote:
>
> The boot-hartid can be a 64bit value on RV64 platforms. Currently,
> the "boot-hartid" in DT is assumed to be 32bit only. This patch
> detects the size of the "boot-hartid" and uses 32bit or 64bit
> FDT reads appropriately.
>
> Signed-off-by: Sunil V L <sunilvl@...tanamicro.com>
> ---
>  drivers/firmware/efi/libstub/riscv-stub.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/firmware/efi/libstub/riscv-stub.c b/drivers/firmware/efi/libstub/riscv-stub.c
> index 9e85e58d1f27..d748533f1329 100644
> --- a/drivers/firmware/efi/libstub/riscv-stub.c
> +++ b/drivers/firmware/efi/libstub/riscv-stub.c
> @@ -29,7 +29,7 @@ static int get_boot_hartid_from_fdt(void)
>  {
>         const void *fdt;
>         int chosen_node, len;
> -       const fdt32_t *prop;
> +       const void *prop;
>
>         fdt = get_efi_config_table(DEVICE_TREE_GUID);
>         if (!fdt)
> @@ -40,10 +40,16 @@ static int get_boot_hartid_from_fdt(void)
>                 return -EINVAL;
>
>         prop = fdt_getprop((void *)fdt, chosen_node, "boot-hartid", &len);
> -       if (!prop || len != sizeof(u32))
> +       if (!prop)
> +               return -EINVAL;
> +
> +       if (len == sizeof(u32))
> +               hartid = (unsigned long) fdt32_to_cpu(*(fdt32_t *)prop);
> +       else if (len == sizeof(u64))
> +               hartid = (unsigned long) fdt64_to_cpu(*(fdt64_t *)prop);

Does RISC-V care about alignment? A 64-bit quantity is not guaranteed
to appear 64-bit aligned in the DT, and the cast violates C alignment
rules, so this should probably used get_unaligned_be64() or something
like that.


> +       else
>                 return -EINVAL;
>
> -       hartid = fdt32_to_cpu(*prop);
>         return 0;
>  }
>
> --
> 2.25.1
>