If S external interrupt is injected to S with mvien & mvip than there is no clear rule to determine its priority

[evgeniy-paltsev]

If we inject S-mode external interrupt (SEI) with virtual interrupts mechanism (mvien & mvip) we need to know it's priority

• to put it to stopi.IPRIO
• to use it for S-mode interrupt arbitration (if several interrupts are pending in sip register)

If we inject SEI interrupt we can't get its priority from IMSIC HW and we can't get its priority from S-mode iprio array (as iprio.SEI (bits 15:8 of iprio2) must be read-only zero).

For other S-mode interrupts the AIA spec defines algorithm to determine priority if corresponding field is 0 in S-mode iprio array:

However such rules can't be used for SEI as it only covers the cases when default priority is either lower or higher than SEI (which is not true if we are checking about SEI itself)

So, what is the rule for SEI interrupt priority in case of injection?

[zhuotianshu]

Hi, I have same question (#91) with yours.
ARC mentioned this problem (https://lists.riscv.org/g/tech-privileged/topic/arc_minutes_2024_09_03/108421694), but the solution seems ambiguous. I am also waiting for a more explicit descirption.

[jhauser-us]

As @zhuotianshu says, this issue is a duplicate of #91. A clearer answer has now been given there.