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

From: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Marc Zyngier <maz@kernel.org>, Atish Patra <atishp@rivosinc.com>,
	Anup Patel <apatel@ventanamicro.com>,
	linux-riscv <linux-riscv@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-efi <linux-efi@vger.kernel.org>,
	Sunil V L <sunil.vl@gmail.com>,
	Sunil V L <sunilvl@ventanamicro.com>
Subject: Re: [PATCH 5/5] riscv/efi_stub: Support for 64bit boot-hartid
Date: Wed, 25 May 2022 18:09:05 +0200	[thread overview]
Message-ID: <1e90b15b-8c73-0de8-2885-1292923b7575@canonical.com> (raw)
In-Reply-To: <CAMj1kXFhEBv7MVCKZuXdx9=hZx3qWbkATdLDwXAe_Zn9Xyx=dg@mail.gmail.com>

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
>>