Hi All,
I would like to start a thread to discuss the topics that should go
into the unix platform specification apart from SBI & PLIC. SBI
specification is already tagged as v0.2 & PLIC specification will
follow.

Here is the current version if unix platform specification.


https://github.com/riscv/riscv-platform-specs/blob/master/riscv-unix.adoc

I think the spec definitely needs to have a lot more content than it
currently has :)

Here are some suggestions. This is just a small list that I can think
of right now. I am pretty sure we need to have more
sections/subsections with more details.

1. Register state requirement:
- S-mode CSR state before entering to S-mode
- GPR state before entering to S-mode (e.g a0 must contain
hartid, a1 must contain DT address)

2. Runtime firmware requirement:
- Platform runtime firmware must implement SBI v0.2
specification. We can avoid legacy implementations in future if we
make this mandatory now. But, I am open to other suggestions
as well.
- RISC-V ISA allows hardware not to implement misaligned
load/store. platform runtime firmware must implement it if it
is not implemented in hardware.
- TIME csr emulation support if not implemented in HW
- HTIMEDELTA csr emulation support (for platforms with hypervisor support)
- This section can link to the SBI specification.

3. Memory requirement
- DRAM start address
- memory model supported
- Boot address alignment requirement (2MB/4MB for 64bit/32bit)
- other requirement ?

4. Interrupt requirement
- What should be PLIC state upon entering S-mdoe
- Can link to the PLIC specifications
- local interrupt controller (CLIC/CLINT) ?

5. I/O devices ?

I am hoping this can initiate the discussion and we can continue that
during the working group meetings as well. The next platform
specification working group is scheduled on 9th June(06/09) 8AM PST.

FYI: The meeting webex link is available in calendar. Let me know if
you have any issues accessing that.


--
Regards,
Atish