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

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Message-ID: <20220526101354.GA19431@sunil-laptop>
Date:   Thu, 26 May 2022 15:43:54 +0530
From:   Sunil V L <sunilvl@...tanamicro.com>
To:     Heinrich Schuchardt <heinrich.schuchardt@...onical.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        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>,
        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, May 25, 2022 at 06:09:05PM +0200, Heinrich Schuchardt wrote:
> On 5/25/22 17:48, Ard Biesheuvel wrote:
> > 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.
> 
> When running in S-mode the SBI handles unaligned access but this has a
> performance penalty.
> 
> We could use fdt64_to_cpu(__get_unaligned_t(fdt64_t, prop)) here.

Thank you very much for the feedback. Have updated as per your
suggestion and sent V2.

Thanks
Sunil

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