[Skiboot] [PATCH 00/12] opal: Improve TOD topology failover.

[Mahesh Jagannath Salgaonkar]

On 04/22/2015 09:36 AM, Stewart Smith wrote:
> Mahesh J Salgaonkar <mahesh at linux.vnet.ibm.com> writes:
>> Once FSP fixes/re-configures the new backup master topology it sends out
>> mailbox command (xE6, s/c 0x06, mod 0) to enable new backup topology.
>> (NOTE: We need to decide how do we handle this on non-FSP based
>> system)
> 
> This would be a PRD related thing. JK?
> 
>> Initial set of patches (1 through 5) sets up the framework to capture the
>> necessary topology info to keep OPAL up-to-date with current topology
>> configurations.
> 
> Is there any reason we need to keep our own copy rather than just
> interrogate TOD_STATUS etc when we need to look things up?
> 

We need this for quick and easy lookup during TOD errors.
Primary/secondary topology configurations on selected chips are assigned
at IPL time and primary/secondary chip id information is passed to OPAL
through HDAT. Further we keep chip role data and backup master's
sync/step network status handy which don't change during all TOD errors.
Keeping this information handy helps us to avoid scanning of all the
chips to identify active/backup master chip id. Not all TOD errors
require TOD topology switch. The primary/secondary topology
configuration do not change until OPAL triggers topology switch at which
point we refresh our data with new master/backup chip ids.

Thanks,
-Mahesh.