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

[Heinrich Schuchardt]

On 5/25/22 17:48, Ard Biesheuvel wrote:
> On Wed, 25 May 2022 at 17:11, Sunil V L <sunilvl@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxx>
> > ---
> >   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.

Best regards

Heinrich

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