Re: Maximum rate value of input power for pmbus device

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

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?


Thanks

Zbigniew