[PATCH] powernv/opal: Handle OPAL_WRONG_STATE error from OPAL fails

[Vipin K Parashar]

Thanks!! for review.

Sending out v2 with  suggested changes.


On Thursday 23 February 2017 09:22 AM, Stewart Smith wrote:
> Michael Ellerman <mpe at ellerman.id.au> writes:
>
>> Stewart Smith <stewart at linux.vnet.ibm.com> writes:
>>
>>> Vipin K Parashar <vipin at linux.vnet.ibm.com> writes:
>>>> On Monday 13 February 2017 06:13 AM, Michael Ellerman wrote:
>>>>> Vipin K Parashar <vipin at linux.vnet.ibm.com> writes:
>>>>>
>>>>>> OPAL returns OPAL_WRONG_STATE for XSCOM operations
>>>>>>
>>>>>> done to read any core FIR which is sleeping, offline.
>>>>> OK.
>>>>>
>>>>> Do we know why Linux is causing that to happen?
>>>> This issue is originally seen upon running STAF (Software Test
>>>> Automation Framework) stress tests and off-lining some cores
>>>> with stress tests running.
>>>>
>>>> It can also be re-created after off-lining few cores and following
>>>> one of below methods.
>>>> 1. Executing Linux "sensors" command
>>>> 2. Reading contents of file /sys/class/hwmon/hwmon0/tempX_input,
>>>>      where X is offline CPU.
>>>>
>>>> Its "opal_get_sensor_data" Linux API that that triggers
>>>> OPAL call "opal_sensor_read", performing XSCOM ops here.
>>>> If core is found sleeping/offline Linux throws up
>>>> "opal_error_code: Unexpected OPAL error" error onto console.
>>>>
>>>> Currently Linux isn't aware about OPAL_WRONG_STATE return code
>>>> from OPAL. Thus it prints "Unexpected OPAL error" message, same
>>>> as it would log for any unknown OPAL return codes.
>>>>
>>>> Seeing this error over console has been a concern for Test and
>>>> would puzzle real user as well. This patch makes Linux aware about
>>>> OPAL_WRONG_STATE return code from OPAL and stops printing
>>>> "Unexpected OPAL error" message onto console for OPAL fails
>>>> with OPAL_WRONG_STATE
>>> Ahh... so this is a DTS sensor, which indeed is just XSCOMs and we
>>> return the xscom_read return code in event of error.
>>>
>>> I would argue that converting to EIO in that instance is probably
>>> correct... or EAGAIN? EAGAIN may be more correct in the situation where
>>> the core is just sleeping.
>>>
>>> What kind of offlining are you doing?
>>>
>>> Arguably, the correct behaviour would be to remove said sensors when the
>>> core is offline.
>> Right, that would be ideal. There appear to be at least two other hwmon
>> drivers that are CPU hotplug aware (coretemp and via-cputemp).
>>
>> But perhaps it's not possible to work out which sensors are attached to
>> which CPU etc., I haven't looked in detail.
> Each core-temp@ sensor has a ibm,pir property, so linking back to what
> core shouldn't be too hard. For mem-temp@ sensors, we have the chip-id.
>
>> In that case changing just opal_get_sensor_data() to handle
>> OPAL_WRONG_STATE would be OK, with a comment explaining that we might be
>> asked to read a sensor on an offline CPU and we aren't able to detect
>> that.
> Agree.
>