Subject: Re: [PATCH] powerpc/powernv : Add support to enable sensor groups
To: Stewart Smith <stewart@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>, linuxppc-dev@lists.ozlabs.org
References: <1511760988-10377-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com>
 <87bmjmzla7.fsf@concordia.ellerman.id.au>
 <06a771ec-fc79-0515-9166-f2a105eb33d0@linux.vnet.ibm.com>
 <87609nxfym.fsf@linux.vnet.ibm.com>
Cc: linux-kernel@vger.kernel.org, ego@linux.vnet.ibm.com,
        akshay.adiga@linux.vnet.ibm.com, svaidy@linux.vnet.ibm.com,
        "linux@roeck-us.net >> Guenter Roeck" <linux@roeck-us.net>
From: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Date: Thu, 21 Dec 2017 10:33:33 +0530
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Hi,

On 12/04/2017 10:11 AM, Stewart Smith wrote:
> Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> writes:
>> On 11/28/2017 05:07 PM, Michael Ellerman wrote:
>>> Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> writes:
>>>
>>>> Adds support to enable/disable a sensor group. This can be used to
>>>> select the sensor groups that needs to be copied to main memory by
>>>> OCC. Sensor groups like power, temperature, current, voltage,
>>>> frequency, utilization can be enabled/disabled at runtime.
>>>>
>>>> Signed-off-by: Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
>>>> ---
>>>> The skiboot patch for the opal call is posted below:
>>>> https://lists.ozlabs.org/pipermail/skiboot/2017-November/009713.html
>>>
>>> Can you remind me why we're doing this with a completely bespoke sysfs
>>> API, rather than using some generic sensors API?
>>>
>>
>> Disabling/Enabling sensor groups is not supported in the current generic sensors
>> API. And also we dont export all type of sensors in HWMON as not all of them are
>> environment sensors (like performance).
> 
> Are there barriers to adding such concepts to the generic sensors API?
> 

Yes.

HWMON does not support attributes for a sensor-group. If we are to extend HWMON
to add new per-sensor attributes to disable/enable, then we need to do either of
the below:

1) If any one of the sensor is disabled then all the sensors belonging to that
group will be disabled. OR

2) To disable a sensor group we need to disable all the sensors belonging to
that group.

Another problem is hwmon categorizes the sensor-groups based on the type of
sensors like power, temp. If OCC allows multiple groups of the same type then
this approach adds some more complexity to the user to identify the sensors
belonging to correct group.

And lastly HWMON does not allow platform specific non-standard sensor groups
like CSM, job-scheduler, profiler.

Thanks and Regards,
Shilpa