Re: [PATCH v6 04/14] riscv: sbi: add FWFT extension interface

[Atish Patra <atish.patra@linux.dev>]

On 5/12/25 1:14 AM, Clément Léger wrote:
>
> On 09/05/2025 02:18, Atish Patra wrote:
>> On 4/24/25 10:31 AM, Clément Léger wrote:
>>> This SBI extensions enables supervisor mode to control feature that are
>>> under M-mode control (For instance, Svadu menvcfg ADUE bit, Ssdbltrp
>>> DTE, etc). Add an interface to set local features for a specific cpu
>>> mask as well as for the online cpu mask.
>>>
>>> Signed-off-by: Clément Léger <cleger@rivosinc.com>
>>> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
>>> ---
>>>    arch/riscv/include/asm/sbi.h | 17 +++++++++++
>>>    arch/riscv/kernel/sbi.c      | 57 ++++++++++++++++++++++++++++++++++++
>>>    2 files changed, 74 insertions(+)
>>>
>>> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
>>> index 7ec249fea880..3bbef56bcefc 100644
>>> --- a/arch/riscv/include/asm/sbi.h
>>> +++ b/arch/riscv/include/asm/sbi.h
>>> @@ -503,6 +503,23 @@ int sbi_remote_hfence_vvma_asid(const struct
>>> cpumask *cpu_mask,
>>>                    unsigned long asid);
>>>    long sbi_probe_extension(int ext);
>>>    +int sbi_fwft_set(u32 feature, unsigned long value, unsigned long
>>> flags);
>>> +int sbi_fwft_set_cpumask(const cpumask_t *mask, u32 feature,
>>> +             unsigned long value, unsigned long flags);
>>> +/**
>>> + * sbi_fwft_set_online_cpus() - Set a feature on all online cpus
>>> + * @feature: The feature to be set
>>> + * @value: The feature value to be set
>>> + * @flags: FWFT feature set flags
>>> + *
>>> + * Return: 0 on success, appropriate linux error code otherwise.
>>> + */
>>> +static inline int sbi_fwft_set_online_cpus(u32 feature, unsigned long
>>> value,
>>> +                       unsigned long flags)
>>> +{
>>> +    return sbi_fwft_set_cpumask(cpu_online_mask, feature, value, flags);
>>> +}
>>> +
>>>    /* Check if current SBI specification version is 0.1 or not */
>>>    static inline int sbi_spec_is_0_1(void)
>>>    {
>>> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
>>> index 1d44c35305a9..d57e4dae7dac 100644
>>> --- a/arch/riscv/kernel/sbi.c
>>> +++ b/arch/riscv/kernel/sbi.c
>>> @@ -299,6 +299,63 @@ static int __sbi_rfence_v02(int fid, const struct
>>> cpumask *cpu_mask,
>>>        return 0;
>>>    }
>>>    +/**
>>> + * sbi_fwft_set() - Set a feature on the local hart
>>> + * @feature: The feature ID to be set
>>> + * @value: The feature value to be set
>>> + * @flags: FWFT feature set flags
>>> + *
>>> + * Return: 0 on success, appropriate linux error code otherwise.
>>> + */
>>> +int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags)
>>> +{
>>> +    return -EOPNOTSUPP;
>>> +}
>>> +
>>> +struct fwft_set_req {
>>> +    u32 feature;
>>> +    unsigned long value;
>>> +    unsigned long flags;
>>> +    atomic_t error;
>>> +};
>>> +
>>> +static void cpu_sbi_fwft_set(void *arg)
>>> +{
>>> +    struct fwft_set_req *req = arg;
>>> +    int ret;
>>> +
>>> +    ret = sbi_fwft_set(req->feature, req->value, req->flags);
>>> +    if (ret)
>>> +        atomic_set(&req->error, ret);
>> What happens when cpuX executed first reported an error but cpuY
>> executed this function later and report success.
>>
>> The error will be masked in that case.
> We actually only set the bit if an error happened (consider it as a
> sticky error bit). So if CPUy reports success, it won't clear the bit.

Ahh yes. I missed that.

> Thanks,
>
> Clément
>
>>> +}
>>> +
>>> +/**
>>> + * sbi_fwft_set_cpumask() - Set a feature for the specified cpumask
>>> + * @mask: CPU mask of cpus that need the feature to be set
>>> + * @feature: The feature ID to be set
>>> + * @value: The feature value to be set
>>> + * @flags: FWFT feature set flags
>>> + *
>>> + * Return: 0 on success, appropriate linux error code otherwise.
>>> + */
>>> +int sbi_fwft_set_cpumask(const cpumask_t *mask, u32 feature,
>>> +                   unsigned long value, unsigned long flags)
>>> +{
>>> +    struct fwft_set_req req = {
>>> +        .feature = feature,
>>> +        .value = value,
>>> +        .flags = flags,
>>> +        .error = ATOMIC_INIT(0),
>>> +    };
>>> +
>>> +    if (feature & SBI_FWFT_GLOBAL_FEATURE_BIT)
>>> +        return -EINVAL;
>>> +
>>> +    on_each_cpu_mask(mask, cpu_sbi_fwft_set, &req, 1);
>>> +
>>> +    return atomic_read(&req.error);
>>> +}
>>> +
>>>    /**
>>>     * sbi_set_timer() - Program the timer for next timer event.
>>>     * @stime_value: The value after which next timer event should fire.