Re: [PATCH v1 1/4] hwmon: (acpi_power_meter) Fix using uninitialized variables

["lihuisong (C)" <lihuisong@huawei.com>]

Hi Guenter,

Can you take a look at my following reply? Looking forward to your reply.

/Huisong


在 2024/11/27 11:43, lihuisong (C) 写道:
> Hi Guenter，
>
> How about the modification as below? But driver doesn't know what the 
> time is to set resource->power_alarm to false.
>
> 在 2024/11/27 0:19, Guenter Roeck 写道:
>> On 11/25/24 23:03, lihuisong (C) wrote:
>>>
>>> 在 2024/11/26 12:04, Guenter Roeck 写道:
>>>> On 11/25/24 17:56, lihuisong (C) wrote:
>>>>> Hi Guente,
>>>>>
>>>>> Thanks for your timely review.
>>>>>
>>>>> 在 2024/11/26 0:03, Guenter Roeck 写道:
>>>>>> On 11/25/24 01:34, Huisong Li wrote:
>>>>>>> The 'power1_alarm' attribute uses the 'power' and 'cap' in the
>>>>>>> acpi_power_meter_resource structure. However, these two fields 
>>>>>>> are just
>>>>>>> updated when user query 'power' and 'cap' attribute, or hardware 
>>>>>>> enforced
>>>>>>> limit. If user directly query the 'power1_alarm' attribute 
>>>>>>> without queryng
>>>>>>> above two attributes, driver will use the uninitialized 
>>>>>>> variables to judge.
>>>>>>> In addition, the 'power1_alarm' attribute needs to update power 
>>>>>>> and cap to
>>>>>>> show the real state.
>>>>>>>
>>>>>>> Signed-off-by: Huisong Li <lihuisong@huawei.com>
>>>>>>> ---
>>>>>>>   drivers/hwmon/acpi_power_meter.c | 10 ++++++++++
>>>>>>>   1 file changed, 10 insertions(+)
>>>>>>>
>>>>>>> diff --git a/drivers/hwmon/acpi_power_meter.c 
>>>>>>> b/drivers/hwmon/acpi_power_meter.c
>>>>>>> index 2f1c9d97ad21..4c3314e35d30 100644
>>>>>>> --- a/drivers/hwmon/acpi_power_meter.c
>>>>>>> +++ b/drivers/hwmon/acpi_power_meter.c
>>>>>>> @@ -396,6 +396,9 @@ static ssize_t show_val(struct device *dev,
>>>>>>>       struct acpi_device *acpi_dev = to_acpi_device(dev);
>>>>>>>       struct acpi_power_meter_resource *resource = 
>>>>>>> acpi_dev->driver_data;
>>>>>>>       u64 val = 0;
>>>>>>> +    int ret;
>>>>>>> +
>>>>>>> +    guard(mutex)(&resource->lock);
>>>>>>>         switch (attr->index) {
>>>>>>>       case 0:
>>>>>>> @@ -423,6 +426,13 @@ static ssize_t show_val(struct device *dev,
>>>>>>>               val = 0;
>>>>>>>           break;
>>>>>>>       case 6:
>>>>>>> +        ret = update_meter(resource);
>>>>>>> +        if (ret)
>>>>>>> +            return ret;
>>>>>>> +        ret = update_cap(resource);
>>>>>>> +        if (ret)
>>>>>>> +            return ret;
>>>>>>> +
>>>>>>>           if (resource->power > resource->cap)
>>>>>>>               val = 1;
>>>>>>>           else
>>>>>>
>>>>>>
>>>>>> While technically correct, the implementation of this attribute 
>>>>>> defeats its
>>>>>> purpose. It is supposed to reflect the current status as reported 
>>>>>> by the
>>>>>> hardware. A real fix would be to use the associated notification 
>>>>>> to set or
>>>>>> reset a status flag, and to report the current value of that flag 
>>>>>> as reported
>>>>>> by the hardware.
>>>>> I know what you mean.
>>>>> The Notify(power_meter, 0x83) is supposed to meet your proposal IIUC.
>>>>> It's good, but it depands on hardware support notification.
>>>>>>
>>>>>> If there is no notification support, the attribute should not 
>>>>>> even exist,
>>>>>> unless there is a means to retrieve its value from ACPI (the 
>>>>>> status itself,
>>>>>> not by comparing temperature values).
>>>>> Currently, the 'power1_alarm' attribute is created just when 
>>>>> platform support the power meter meassurement(bit0 of the 
>>>>> supported capabilities in _PMC).
>>>>> And it doesn't see if the platform support notifications.
>>>>>  From the current implementation of this driver, this sysfs can 
>>>>> also reflect the status by comparing power and cap,
>>>>> which is good to the platform that support hardware limit from 
>>>>> some out-of-band mechanism but doesn't support any notification.
>>>>>
>>>>
>>>> The point is that this can also be done from userspace. Hardware 
>>>> monitoring drivers
>>>> are supposed to provide hardware attributes, not software 
>>>> attributes derived from it.
>>>>
>>> So this 'power1_alarm' attribute can be exposed when platform 
>>> supports hardware enforced limit and notifcations when the hardware 
>>> limit is enforced, right?
>>> If so, we have to change the condition that driver creates this 
>>> sysfs interface.
>>
>> This isn't about enforcing anything, it is about reporting an alarm
>> if the power consumed exceeds the maximum configured.
>>
> -->
>
> index 2f1c9d97ad21..b436ebd863e6
> --- a/drivers/hwmon/acpi_power_meter.c
> +++ b/drivers/hwmon/acpi_power_meter.c
> @@ -84,6 +84,7 @@ struct acpi_power_meter_resource {
>         u64             power;
>         u64             cap;
>         u64             avg_interval;
> +       bool            power_alarm;
>         int                     sensors_valid;
>         unsigned long           sensors_last_updated;
>         struct sensor_device_attribute  sensors[NUM_SENSORS];
> @@ -396,6 +397,9 @@ static ssize_t show_val(struct device *dev,
>         struct acpi_device *acpi_dev = to_acpi_device(dev);
>         struct acpi_power_meter_resource *resource = 
> acpi_dev->driver_data;
>         u64 val = 0;
> +       int ret;
> +
> +       guard(mutex)(&resource->lock);
>
>         switch (attr->index) {
>         case 0:
> @@ -423,10 +427,21 @@ static ssize_t show_val(struct device *dev,
>                         val = 0;
>                 break;
>         case 6:
> -               if (resource->power > resource->cap)
> -                       val = 1;
> -               else
> -                       val = 0;
> +               /* report alarm status based on the notification if 
> support. */
> +               if (resource->caps.flags & POWER_METER_CAN_NOTIFY) {
> +                       val = resource->power_alarm;
> +               } else {
> +                       ret = update_meter(resource);
> +                       if (ret)
> +                               return ret;
> +                       ret = update_cap(resource);
> +                       if (ret)
> +                               return ret;
> +                       if (resource->power > resource->cap)
> +                               val = 1;
> +                       else
> +                               val = 0;
> +               }
>                 break;
>         case 7:
>         case 8:
> @@ -853,6 +868,7 @@ static void acpi_power_meter_notify(struct 
> acpi_device *device, u32 event)
>                 sysfs_notify(&device->dev.kobj, NULL, 
> POWER_AVG_INTERVAL_NAME);
>                 break;
>         case METER_NOTIFY_CAPPING:
> +               resource->power_alarm = true;
>                 sysfs_notify(&device->dev.kobj, NULL, POWER_ALARM_NAME);
>                 dev_info(&device->dev, "Capping in progress.\n");
>                 break;
>
>> .
>
> .