pussuw commented on pull request #5782:
URL: https://github.com/apache/incubator-nuttx/pull/5782#issuecomment-1077331325
> Why not implement OpenSBI API in M-mode required by S-mode NuttX directly?
I think is more simple and general than a private MiniSBI. We can write from
scratch in M-mode NuttX without link OpenSBI package and implement function and
argument which actually used by S-mode NuttX. The benefit of this approach is:
>
> 1. One copy code in S-mode can work with M-mode NuttX or other OpenSBI
compliant implementation
>
> 2. M-mode NuttX can enable your minimal OpenSBI implementation, or
switch to the full feature OpenSBI package
>
>
> Both side get the flexibility and avoid to lock to some special
implementation.
It can be done. The skeleton for this pretty much exists in this patch
already.
The abstraction point in this case would be the riscv_mcall.c module:
```
void riscv_mcall_ack_timer(void)
{
mcall0(MCALL_ACK_TIMER);
}
```
Instead of directly calling mcall0 it would call some "openSBI_wrap_timerxx"
function, which would ecall into OpenSBI which would do the work.
This requires obviously that OpenSBI is built & linked with NuttX (or
separately) and placed into memory somehow. NuttX would then be provided as a
payload binary to OpenSBI. Adding this infrastructure is a lot of work.
> Actually, you can split the patch into at least two part:
>
> 1. M-mode add the minimal OpenSBI implementation
>
> 2. S-mode implementation
Yes, of course. I can do the split.
At this point I would like to clarify, that the task given to me is "enable
CONFIG_BUILD_KERNEL=y" for RISC-V on MPFS platform, and S-mode is just one of
the requirements to get that done. What this patch includes does not break any
existing code or what we already have. It was made just as an enabler to get
CONFIG_BUILD_KERNEL working with the minimal amount of extra effort.
I can do the abstraction / enabler to use OpenSBI instead of my "MiniSBI"
but at this point I will not implement full OpenSBI support to NuttX as it is a
lot of extra work and does not bring me any closer to the target / task I have
been given.
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