[Skiboot] [PATCH v5 5/5] SBE: Add timer support

Vasant Hegde hegdevasant at linux.vnet.ibm.com
Mon Jul 24 23:51:04 AEST 2017

On 07/24/2017 04:05 AM, Benjamin Herrenschmidt wrote:
> On Sun, 2017-07-23 at 17:00 +0530, Vasant Hegde wrote:
>> SBE on P9 provides one shot programmable timer facility. We can use this
>> to implement OPAL timers and hence limit the reliance on the Linux
>> heartbeat (similar to HW timer facility provided by SLW on P8).
>> Design:
>>   - We will continue to run Linux heartbeat.
>>   - Each chip has SBE. This patch always schedules timer on SBE on master chip.
>>   - Timer MBOX has two options (start/stop timer). We cannot modify inflight
>>     timer message. Hence we reschedule timer if new timer value is greater than
>>     current time and less than scheduled timer value.
> Can't they fix their interface to match what we need instead ?

We had asked them .. but they told they are not supporting multiple timer.

So if new timer request is < inflight timer then we have to cancel and schedule 
new timer.

>>   - SBE expects timeout value in milliseconds. We track timeout value in TB.
>>     Hence we convert tb to milliseconds before sending request to SBE.
> This is WAYYYYYY to coarse resolution. We want microseconds. They need
> to fix their stuff.

We will check with FW folks on this.


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