[Skiboot] [RFC] occ: Add support for OCC inband sensors

[Cédric Le Goater]

On 03/10/2017 01:24 AM, Stewart Smith wrote:
> Andrew Jeffery <andrew at aj.id.au> writes:
>> On Thu, 2017-03-09 at 13:44 +0100, Cédric Le Goater wrote:
>>> Hello Shilpasri,
>>>
>>> Thanks for the write up on the OCC sensors. Nice and detailed.
>>>
>>> On the overall design, I think this is exposing too much HW details 
>>> to Linux. I am not sure Linux should even know about OCC or where
>>> the sensors are coming from. Even if this is doable, I would not 
>>> let the kernel loop on the OCC data to collect which sensors are
>>> available. What is being done under :
>>>
>>> 	arch/powerpc/platforms/powernv/opal-occ-sensors.c
>>>
>>> in the Linux driver should be in the firmware IHMO. 
>>>
>>> skiboot should hide the gory details and expose in the device 
>>> tree sensor nodes collected from the different available sources: 
>>> FSP, BMC, OCC, DTS, etc. 
>>>
>>> There is a framework in place in skiboot for that, which may be, 
>>> needs some tuning to add OCC support. But the good thing about it, 
>>> is that the Linux driver comes for free in *all* Linux distros now.
>>
>> I spoke with Stewart a while back about how we should expose sensors to
>> Linux and we reached the same conclusions as Cedric. Lets keep the OCC
>> details contained in the firmware.
> 
> Yep. OCC is merely an implementation detail.
> 
> I'd argue that all sensors should be readable through the OPAL calls. As
> an optimisation, we could add the ability for some opal sensors to be
> read directly from an address by the kernel.

And  we would expose in the device tree an address to read the 
value from ? we would need a new reserved region I suppose.  

C.

 
> But yeah, for these sensors, existing kernels should "just work" by
> using the existing OPAL calls.
>