[PATCH V4] cxl: Add support for ASB_Notify on POWER9

[Vaibhav Jain]

christophe lombard <clombard at linux.vnet.ibm.com> writes:

> Le 20/12/2017 à 09:46, Vaibhav Jain a écrit :
>>> In fact, it does not matter. I don't know what the userspace could do
>>> with this value.
>> Without libcxl knowing the tidr value, it cannot enforce the condition
>> that only threads that have called attach can issue 'wait' on the right
>> context.
>> 
>> Also AFU can selectively ask PSL to issue asb_notify to a specific
>> thread via the PSL interface. Without userspace knowing the tidr value
>> it might not be easy for it to give this value to AFU through a Problem
>> State Area register.
>> 
>
> Don't forget that The ASB_Notify will use LPID:PID:TID tuple found
> in the Process Element Entry.
> The AFU may optionally provide a TID on AxH_CEA[40:55] (AxH_CEA[39]
> must be set to indicate an AFU provided TID)
> If AxH_CEA[39] == 1’b0 then Process Element information
> (LPID:PID:TID) is used to generate the PCIe address.
> If AxH_CEA[39] == 1’b1then the LPID:PID are taken from the PEE
> while the TID is taken from AxH_-CEA[40:55]

Agree and that was the point I was trying to make when I said that AFU
can selectivly issue asb_notify to a thread. Without userspace threads
knowing their tidr libcxl would let any thread issue the 'wait'
instruction that may cause unpredictable results.

-- 
Vaibhav Jain <vaibhav at linux.vnet.ibm.com>
Linux Technology Center, IBM India Pvt. Ltd.