Re: [PATCH v5 3/8] ACPI: CPPC: Rename cppc_get_perf() to cppc_get_reg_val()

["zhenglifeng (A)" <zhenglifeng1@huawei.com>]

On 2025/3/13 3:54, Rafael J. Wysocki wrote:

> On Thu, Feb 6, 2025 at 2:14 PM Lifeng Zheng <zhenglifeng1@huawei.com> wrote:
>>
>> Rename cppc_get_perf() to cppc_get_reg_val() as a generic function to read
>> cppc registers. And extract the operations if register is in pcc out as
>> cppc_get_reg_val_in_pcc(). Without functional change.
> 
> This should be split into two patches IMV.

Yes. That makes sense. Thanks.

> 
>> Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
>> ---
>>  drivers/acpi/cppc_acpi.c | 66 +++++++++++++++++++++-------------------
>>  1 file changed, 35 insertions(+), 31 deletions(-)
>>
>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>> index db22f8f107db..3c9c4ce2a0b0 100644
>> --- a/drivers/acpi/cppc_acpi.c
>> +++ b/drivers/acpi/cppc_acpi.c
>> @@ -1189,48 +1189,52 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>>         return ret_val;
>>  }
>>
>> -static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
>> +static int cppc_get_reg_val_in_pcc(int cpu, struct cpc_register_resource *reg, u64 *val)
>>  {
>> -       struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
>> -       struct cpc_register_resource *reg;
>> +       int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
>> +       struct cppc_pcc_data *pcc_ss_data = NULL;
>> +       int ret;
>>
>> -       if (!cpc_desc) {
>> -               pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
>> +       if (pcc_ss_id < 0) {
>> +               pr_debug("Invalid pcc_ss_id\n");
>>                 return -ENODEV;
>>         }
>>
>> -       reg = &cpc_desc->cpc_regs[reg_idx];
>> +       pcc_ss_data = pcc_data[pcc_ss_id];
>>
>> -       if (IS_OPTIONAL_CPC_REG(reg_idx) && !CPC_SUPPORTED(reg)) {
>> -               pr_debug("CPC register (reg_idx=%d) is not supported\n", reg_idx);
>> -               return -EOPNOTSUPP;
>> -       }
> 
> I'm not a big fan of the IS_OPTIONAL_CPC_REG() macro.  I'm not
> convinced at all that it adds any value above (and in the next patch
> for that matter) and the message printing the register index is just
> plain unuseful to anyone who doesn't know how to decode it.

With this index, it is easier to locate problems. This is what a "pr_debug"
for, isn't it?

> 
> If CPC_SUPPORTED(reg) is not true, the register cannot be used AFAICS
> regardless of what IS_OPTIONAL_CPC_REG() has to say about it.

The name "CPC_SUPPORTED" may be a little confused. Actually, in ACPI 6.5,
only optional _CPC package fields that are not supported by the platform
should be encoded as 0 intergers or NULL registers. A mandatory field as a
0 interger is valid. So If I wanted to make this function as a generic one
to read cppc registers, it would have been more reasonable to do this
IS_OPTIONAL_CPC_REG() check before CPC_SUPPORTED().

> 
>> +       down_write(&pcc_ss_data->pcc_lock);
>>
>> -       if (CPC_IN_PCC(reg)) {
>> -               int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpunum);
>> -               struct cppc_pcc_data *pcc_ss_data = NULL;
>> -               int ret;
>> +       if (send_pcc_cmd(pcc_ss_id, CMD_READ) >= 0)
>> +               ret = cpc_read(cpu, reg, val);
>> +       else
>> +               ret = -EIO;
>>
>> -               if (pcc_ss_id < 0) {
>> -                       pr_debug("Invalid pcc_ss_id\n");
>> -                       return -ENODEV;
>> -               }
>> +       up_write(&pcc_ss_data->pcc_lock);
>>
>> -               pcc_ss_data = pcc_data[pcc_ss_id];
>> +       return ret;
>> +}
>>
>> -               down_write(&pcc_ss_data->pcc_lock);
>> +static int cppc_get_reg_val(int cpu, enum cppc_regs reg_idx, u64 *val)
>> +{
>> +       struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
>> +       struct cpc_register_resource *reg;
>>
>> -               if (send_pcc_cmd(pcc_ss_id, CMD_READ) >= 0)
>> -                       ret = cpc_read(cpunum, reg, perf);
>> -               else
>> -                       ret = -EIO;
>> +       if (!cpc_desc) {
>> +               pr_debug("No CPC descriptor for CPU:%d\n", cpu);
>> +               return -ENODEV;
>> +       }
>>
>> -               up_write(&pcc_ss_data->pcc_lock);
>> +       reg = &cpc_desc->cpc_regs[reg_idx];
>>
>> -               return ret;
>> +       if (IS_OPTIONAL_CPC_REG(reg_idx) && !CPC_SUPPORTED(reg)) {
>> +               pr_debug("CPC register (reg_idx=%d) is not supported\n", reg_idx);
>> +               return -EOPNOTSUPP;
>>         }
>>
>> -       return cpc_read(cpunum, reg, perf);
>> +       if (CPC_IN_PCC(reg))
>> +               return cppc_get_reg_val_in_pcc(cpu, reg, val);
>> +
>> +       return cpc_read(cpu, reg, val);
>>  }
>>
>>  /**
>> @@ -1242,7 +1246,7 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
>>   */
>>  int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
>>  {
>> -       return cppc_get_perf(cpunum, DESIRED_PERF, desired_perf);
>> +       return cppc_get_reg_val(cpunum, DESIRED_PERF, desired_perf);
>>  }
>>  EXPORT_SYMBOL_GPL(cppc_get_desired_perf);
>>
>> @@ -1255,7 +1259,7 @@ EXPORT_SYMBOL_GPL(cppc_get_desired_perf);
>>   */
>>  int cppc_get_nominal_perf(int cpunum, u64 *nominal_perf)
>>  {
>> -       return cppc_get_perf(cpunum, NOMINAL_PERF, nominal_perf);
>> +       return cppc_get_reg_val(cpunum, NOMINAL_PERF, nominal_perf);
>>  }
>>
>>  /**
>> @@ -1267,7 +1271,7 @@ int cppc_get_nominal_perf(int cpunum, u64 *nominal_perf)
>>   */
>>  int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
>>  {
>> -       return cppc_get_perf(cpunum, HIGHEST_PERF, highest_perf);
>> +       return cppc_get_reg_val(cpunum, HIGHEST_PERF, highest_perf);
>>  }
>>  EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>>
>> @@ -1280,7 +1284,7 @@ EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>>   */
>>  int cppc_get_epp_perf(int cpunum, u64 *epp_perf)
>>  {
>> -       return cppc_get_perf(cpunum, ENERGY_PERF, epp_perf);
>> +       return cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
>>  }
>>  EXPORT_SYMBOL_GPL(cppc_get_epp_perf);
>>
>> --
>> 2.33.0
>>
>>
>