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

Sunil V L
2022-05-26T10:14:04Z

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@ventanamicro.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@ventanamicro.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
> > >
>