linux-kernel - Re: [PATCH v3 2/2] hwmon: acpi_power_meter: convert to hwmon_device_register_with

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Date:   Sat, 21 May 2022 06:52:15 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     LABBE Corentin <clabbe@...libre.com>
Cc:     jdelvare@...e.com, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org, Zhang Rui <rui.zhang@...el.com>
Subject: Re: [PATCH v3 2/2] hwmon: acpi_power_meter: convert to
 hwmon_device_register_with_info

On 5/16/22 05:21, Guenter Roeck wrote:
> On 5/15/22 23:21, LABBE Corentin wrote:
>> Le Sun, May 15, 2022 at 05:29:54PM -0700, Guenter Roeck a écrit :
>>> On 5/15/22 12:36, LABBE Corentin wrote:
>>>> Le Wed, May 11, 2022 at 07:10:29PM -0700, Guenter Roeck a écrit :
>>>>> Corentin,
>>>>>
>>>>> On 5/8/22 23:30, Corentin Labbe wrote:
>>>>>> Booting lead to a hwmon_device_register() is deprecated. Please convert the driver to use hwmon_device_register_with_info().
>>>>>> So let's convert the driver to use hwmon_device_register_with_info().
>>>>>>
>>>>>> Signed-off-by: Corentin Labbe <clabbe@...libre.com>
>>>>>> ---
>>>>> [ ... ]
>>>>>
>>>>>> @@ -836,20 +740,20 @@ static void acpi_power_meter_notify(struct acpi_device *device, u32 event)
>>>>>>             if (res)
>>>>>>                 break;
>>>>>> -        remove_attrs(resource);
>>>>>> +        remove_domain_devices(resource);
>>>>>>             setup_attrs(resource);
>>>>>
>>>>> Zhang Rui found an interesting problem with this code:
>>>>> It needs a call to sysfs_update_groups(hwmon_dev->groups)
>>>>> to update sysfs attribute visibility, probably between
>>>>> remove_domain_devices() and setup_attrs().
>>>>>
>>>>>>             break;
>>>>>>         case METER_NOTIFY_TRIP:
>>>>>> -        sysfs_notify(&device->dev.kobj, NULL, POWER_AVERAGE_NAME);
>>>>>> +        hwmon_notify_event(&device->dev, hwmon_power, hwmon_power_average, 0);
>>>>>
>>>>> ... which makes realize: The notification device should be the hwmon device.
>>>>> That would be resource->hwmon_dev, not the acpi device.
>>>>>
>>>>
>>>> Hello
>>>>
>>>> Since my hardware lacks capabilities testing this, I have emulated it on qemu:
>>>> https://github.com/montjoie/qemu/commit/320f2ddacb954ab308ef699f66fca6313f75bc2b
>>>>
>>>> I have added a custom ACPI _DBX method for triggering some ACPI state change. (like config change, like enabling CAP).
>>>>
>>>> For testing config change I have tried lot of way:
>>>>                   res = read_capabilities(resource);
>>>> @@ -742,18 +758,22 @@ static void acpi_power_meter_notify(struct acpi_device *device, u32 event)
>>>>                   remove_domain_devices(resource);
>>>>                   setup_attrs(resource);
>>>> +               res = sysfs_update_groups(&resource->hwmon_dev->kobj, acpi_power_groups);
>>>> +               res = sysfs_update_groups(&resource->acpi_dev->dev.kobj, acpi_power_groups);
>>>> +               res = hwmon_notify_event(resource->hwmon_dev, hwmon_power, hwmon_power_cap, 0);
>>>> +               res = hwmon_notify_event(resource->hwmon_dev, hwmon_power, hwmon_power_average, 0);
>>>
>>> Did you add a debug log here ?
>>
>> Yes I added debug log to check what is called.
>>
>>>
>>> acpi_power_groups would be the wrong parameter for sysfs_update_groups().
>>> It would have to be resource->hwmon_dev->groups.
>>>
>>
>> Even with that, no call to is_visible:
>> @@ -742,18 +758,22 @@ static void acpi_power_meter_notify(struct acpi_device *device, u32 event)
>>                  remove_domain_devices(resource);
>>                  setup_attrs(resource);
>> +               res = sysfs_update_groups(&resource->hwmon_dev->kobj, resource->hwmon_dev->groups);
>> +               res = sysfs_update_groups(&resource->acpi_dev->dev.kobj, resource->hwmon_dev->groups);
>> +               res = hwmon_notify_event(resource->hwmon_dev, hwmon_power, hwmon_power_cap, 0);
>> +               res = hwmon_notify_event(resource->hwmon_dev, hwmon_power, hwmon_power_average, 0);
>>                  break;
>>
>> I checked drivers/hwmon/hwmon.c is seems that is_visible is only called by gen_attr/gen_attrs which is only called by __hwmon_create_attrs and then by registers functions.
>> So perhaps it explain why it is never called.
> 
> Ah yes, you are correct. Sorry, it has been too long ago that I wrote that code.
> Effectively that means we'll have to rework the hwmon core to generate attributes
> anyway and leave it up to the driver core to call the is_visible function.
> 

Attached is an outline of what would be needed in the hwmon core.
Completely untested. I wonder if it may be easier to always
create all attributes and have them return -ENODATA if not
supported.

Guenter
View attachment "0001-hwmon-Implement-hwmon_update_groups.patch" of type "text/x-patch" (6332 bytes)