Re: [PATCH 0/1] SBI: Introduce Physical Memory Protection Extension
On Tue, 2020-03-10 at 07:25 -0700, Bin Meng wrote:
S-mode software needs a way to know memory used by SBI firmware soLet's continue the discussion here as it has a wider audience than
github PR. I have also cc'd all the possible stakeholders.
The other alternatives propsed so far
1. Just parse the deveice tree node in S-mode software.
Pros: No additional SBI extensions are required.
Cons: U-Boot is responsible for copying the reserved-memory node from
the DT passed by OpenSBI and set it to the final DT if it is a
different one. OpenSBI also need to provide the DT where the previous
stage (FSBL/U-Boot SPL) doesn't provide a DT.
IMHO, this is not a very difficult problem to solve. The U-Boot
implementation is available here (just ~40 lines of code).
2. Trap-n-Emulate PMP CSR reads from S-mode. The details are available
Pros: No SBI extension or prior DTB fixup required in U-Boot.
Cons: As PMP extensions proposals are already in place, this may need
to be extended. Privilege spec may need to be modified to explicitly
say that M-mode can provide PMP csr emulation.
Any thoughts ?