[Skiboot] [PATCH] doc: Document ibm,heartbeat-ms

[Stewart Smith]

Oliver <oohall at gmail.com> writes:
> On Tue, Apr 3, 2018 at 2:57 PM, Stewart Smith <stewart at linux.ibm.com> wrote:
>> and by 'document', I mean 'gather a few extra minor bits of breadcrumbs
>> of clues as to what, when and why this thing exists'.
>>
>> Signed-off-by: Stewart Smith <stewart at linux.ibm.com>
>> ---
>>  doc/device-tree/ibm,opal.rst | 21 +++++++++++++++++++++
>>  1 file changed, 21 insertions(+)
>>
>> diff --git a/doc/device-tree/ibm,opal.rst b/doc/device-tree/ibm,opal.rst
>> index 932f41d05cde..2fa446ddef04 100644
>> --- a/doc/device-tree/ibm,opal.rst
>> +++ b/doc/device-tree/ibm,opal.rst
>> @@ -50,3 +50,24 @@ Top level ibm,opal node
>>                 opal-runtime-size = <0x0 0x9a00000>;
>>                 phandle = <0x10000003>;
>>      };
>> +
>> +.. ibm-heartbeat-ms:
>> +
>> +ibm,heartbeat-ms
>> +^^^^^^^^^^^^^^^^
>> +
>> +.. code-block:: dts
>> +
>> +   ibm,opal {
>> +               ibm,heartbeat-ms = <0x7d0>;
>> +   }
>> +
>> +
>> +Any OS targetting POWER9 processors *must* respect `ibm,heartbeat-ms`.
>> +
>> +Linux kernels prior to v4.1-rc1 would ignore `ibm,heartbeat-ms`. These only
>> +supported POWER8 systems.
>> +
>> +On the earliest POWER8 OPAL systems, there was `ibm,heartbeat-freq` instead.
>> +However, no OS at the time ever looked at that value, so it can be ignored
>> +by any new operating systems.
>
> Doesn't this set the interval between calls to OPAL_POLL_EVENTS? I
> think as a side effect
> we also run the pollers inside of skiboot so you need it to make
> centaur I2C work too.

> We should probably document that :)

I'm pretty sure it's documented in hw/i2c.c[1]

[1] Yes, I'm aware the source code is in hw/p8-i2c.c - I'm attempting to
    be funny. Not ha-ha funny though.
-- 
Stewart Smith
OPAL Architect, IBM.