arch-riscv: Make ISA class the source of CSR info
Previously, all components assume the info in arch/riscv/regs/misc.hh to
be the single source of CSR info. That will however make adding
non-standard CSRs difficult as all those CSRs will need to go into the
same header & data structure and might conflict with each other.
In this CL, we add two new functions to the ISA class that provide
information about CSR. The rationale is that, the ISA class is already
the owner of CSR data, so it'll also be in a better position to provide
necessary CSR metadata. With the change, we can create two CPU models
with slightly different custom CSRs easily by creating two derived
RiscvISA classes and overriding the two functions.
We assume that, any customized CSR set is still compatible with standard
CSRs, so we could still utilize the same global map if only standard
CSRs are accessed in the use case.
Note that this does not necessarily mean you cannot or should not add
your customize CSRs into the MiscRegIndex enum. You'll usually still
required to do that to give each CSR an unique id. However, the ability
to override CSRDataMap/CSRMaskMap provide an opportunity to remap how
the CSR index encoded in the instruction maps to CSR, and also give you
a chance to make the read/write logic of certain custom CSRs different.
Change-Id: I168188bdb1baed11cb3e217eb021f289a13bb036
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62891
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
4 files changed
