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Subject: Re: [PATCH 0/3] Add support to disable sensor groups in P9
To:     Guenter Roeck <linux@roeck-us.net>
References: <1521716075-807-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com>
 <20180515150205.GA29321@roeck-us.net>
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 <56bba97b-c6ee-e7a1-136c-a2236437484a@roeck-us.net>
Cc:     mpe@ellerman.id.au, linuxppc-dev@lists.ozlabs.org,
        linux-hwmon@vger.kernel.org, linux-kernel@vger.kernel.org,
        stewart@linux.vnet.ibm.com
From:   Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com>
Date:   Fri, 18 May 2018 09:33:57 +0530
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On 05/17/2018 06:08 PM, Guenter Roeck wrote:
> On 05/16/2018 11:10 PM, Shilpasri G Bhat wrote:
>>
>>
>> On 05/15/2018 08:32 PM, Guenter Roeck wrote:
>>> On Thu, Mar 22, 2018 at 04:24:32PM +0530, Shilpasri G Bhat wrote:
>>>> This patch series adds support to enable/disable OCC based
>>>> inband-sensor groups at runtime. The environmental sensor groups are
>>>> managed in HWMON and the remaining platform specific sensor groups are
>>>> managed in /sys/firmware/opal.
>>>>
>>>> The firmware changes required for this patch is posted below:
>>>> https://lists.ozlabs.org/pipermail/skiboot/2018-March/010812.html
>>>>
>>>
>>> Sorry for not getting back earlier. This is a tough one.
>>>
>>
>> Thanks for the reply. I have tried to answer your questions according to my
>> understanding below:
>>
>>> Key problem is that you are changing the ABI with those new attributes.
>>> On top of that, the attributes _do_ make some sense (many chips support
>>> enabling/disabling of individual sensors), suggesting that those or
>>> similar attributes may or even should at some point be added to the ABI.
>>>
>>> At the same time, returning "0" as measurement values when sensors are
>>> disabled does not seem like a good idea, since "0" is a perfectly valid
>>> measurement, at least for most sensors.
>>
>> I agree.
>>
>>>
>>> Given that, we need to have a discussion about adding _enable attributes to
>>> the ABI
>>
>>> what is the scope,
>> IIUC the scope should be RW and the attribute is defined for each supported
>> sensor group
>>
> 
> That is _your_ need. I am not aware of any other chip where a per-sensor group
> attribute would make sense. The discussion we need has to extend beyond the need
> of a single chip.
> 
> Guenter
> 


Is it okay if the ABI provides provision for both types of attribute
power_enable and powerX_enable. And is it okay to decide which type of attribute
to be used by the capability provided by the hwmon chip?


- Shilpa

>>> when should the attributes exist and when not,
>> We control this currently via device-tree
>>
>>> do we want/need power_enable or powerX_enable or both, and so on), and
>> We need power_enable right now
>>
>>> what to return if a sensor is disabled (such as -ENODATA).
>> -ENODATA sounds good.
>>
>> Thanks and Regards,
>> Shilpa
>>
>>   Once we have an
>>> agreement, we can continue with an implementation.
>>>
>>> Guenter
>>>
>>>> Shilpasri G Bhat (3):
>>>>    powernv:opal-sensor-groups: Add support to enable sensor groups
>>>>    hwmon: ibmpowernv: Add attributes to enable/disable sensor groups
>>>>    powernv: opal-sensor-groups: Add attributes to disable/enable sensors
>>>>
>>>>   .../ABI/testing/sysfs-firmware-opal-sensor-groups  |  34 ++++++
>>>>   Documentation/hwmon/ibmpowernv                     |  31 ++++-
>>>>   arch/powerpc/include/asm/opal-api.h                |   4 +-
>>>>   arch/powerpc/include/asm/opal.h                    |   2 +
>>>>   .../powerpc/platforms/powernv/opal-sensor-groups.c | 104 ++++++++++++-----
>>>>   arch/powerpc/platforms/powernv/opal-wrappers.S     |   1 +
>>>>   drivers/hwmon/ibmpowernv.c                         | 127
>>>> +++++++++++++++++++--
>>>>   7 files changed, 265 insertions(+), 38 deletions(-)
>>>>   create mode 100644
>>>> Documentation/ABI/testing/sysfs-firmware-opal-sensor-groups
>>>>
>>>> -- 
>>>> 1.8.3.1
>>>>
>>>> -- 
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>>>
>>
>>
>