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

Heinrich Schuchardt
2022-05-25T16:09:13Z

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.

Best regards

Heinrich

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