Re: Maximum rate value of input power for pmbus device

[zlukwins <zbigniew.lukwinski@linux.intel.com>]

On 7/8/20 3:33 PM, Guenter Roeck wrote:
> On 7/8/20 3:50 AM, zlukwins wrote:
>> On 6/29/20 6:59 PM, Guenter Roeck wrote:
>>> +linux-hwmon@vger.kernel.org
>>>
>>> On Mon, Jun 29, 2020 at 08:31:11AM +0200, zlukwins wrote:
>>>> Hi,
>>>>
>>>>
>>>> I am OpenBMC FW developer working currently on some power measurement stuff.
>>>>
>>>> I would like to have maximum rated input power for pmubus device available
>>>> in hwmon sysfs. This value is read by MFR_PIN_MAX command:
>>>>
>>>> /MFR_PIN_MAX//
>>>> //The MFR_PIN_MIN command sets or retrieves the maximum rated value, in
>>>> watts, of//
>>>> //the input power./
>>> Interesting typo in the PMBus specification. Yes, it really does associate
>>> MFR_PIN_MIN - which doesn't seem to exist - with the maximum rated output
>>> power.
>>>> And I wondering which attribute shell be used to expose that value in sysfs.
>>>> I went through documentation
>>>> (https://www.kernel.org/doc/Documentation/hwmon/sysfs-interface) and found
>>>> the following:
>>>>
>>>> power[1-*]_max            Maximum power.
>>>>                  Unit: microWatt
>>>>                  RW
>>>>
>>>> But it looks like it is already occupied by PIN_OP_WARN_LIMIT.
>>>>
>>>> Maybe new attribute shall be used? If so how to call that?
>>>>
>>> None of the standard attributes reports (or is supposed to report) rated
>>> values, so we can not just use any of those.
>>>
>>> Also, we can not just add a single attribute to handle this situation,
>>> for the simple reason that there are many more similar attributes.
>>> PMBus specifies (this is from version 1.3.1):
>>>
>>> MFR_VIN_MIN
>>> MFR_VIN_MAX
>>> MFR_IIN_MAX
>>> MFR_PIN_MAX
>>> MFR_VOUT_MIN
>>> MFR_VOUT_MAX
>>> MFR_IOUT_MAX
>>> MFR_POUT_MAX
>>> MFR_TAMBIENT_MAX
>>> MFR_TAMBIENT_MIN
>>> MFR_MAX_TEMP_{1,2.3}
>>>
>>> All those report rated values. I do see the need/desire for reporting such
>>> information. The only real solution I can see is to add a new set of
>>> attributes to the hwmon ABI. Something like:
>>>
>>>      currentX_rated_min    # for consistency
>>>      currentX_rated_max
>>>      inX_rated_min
>>>      inX_rated_max
>>>      powerX_rated_min    # for consistency
>>>      powerX_rated_max
>>>      tempX_rated_min
>>>      tempX_rated_max
>>> plus maybe, for consistency:
>>>      humidityX_rated_min
>>>      humidityX_rated_max
>>>
>>> Those would be read-only attributes.
>>>
>>> Thoughts, comments, feedback anyone ?
>>>
>>> Thanks,
>>> Guenter
>>
>> I really like your proposition but I guess we need to wait few more days for the feedback.
>>
>> But have some questions here.
>>
>> What about potential next steps when we all agreed to follow that approach. Should documentation modification reach upstream repository first and then e.g. pmbus hwmon module implementation?
>>
> We'll need a series of patches. One to amend the documentation, one to add
> the necessary code to the hwmon core (so that the core supports it with
> the _with_info API), one to add support to the PMBus core, and one each
> to add support to affected drivers.
>
> Once this is all complete, the lm-sensors package should be updated
> as well.
>
> Guenter

Do you think we need to wait for feedback or maybe we could implement 
with your proposition? Maybe I could start working on patches?


Thanks

Zbigniew