target/riscv: deprecate the 'any' CPU type

The 'any' CPU type was introduced in commit dc5bd18 ("RISC-V CPU
Core Definition"), being around since the beginning. It's not an easy
CPU to use: it's undocumented and its name doesn't tell users much about
what the CPU is supposed to bring. 'git log' doesn't help us either in
knowing what was the original design of this CPU type.

The closest we have is a comment from Alistair [1] where he recalls from
memory that the 'any' CPU is supposed to behave like the newly added
'max' CPU. He also suggested that the 'any' CPU should be removed.

The default CPUs are rv32 and rv64, so removing the 'any' CPU will have
impact only on users that might have a script that uses '-cpu any'.
And those users are better off using the default CPUs or the new 'max'
CPU.

We would love to just remove the code and be done with it, but one does
not simply remove a feature in QEMU. We'll put the CPU in quarantine
first, letting users know that we have the intent of removing it in the
future.

[1] https://lists.gnu.org/archive/html/qemu-devel/2023-07/msg02891.html

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-ID: <20230901194627.1214811-13-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

docs/about/deprecated.rst

@@ -365,6 +365,18 @@ QEMU's ``vhost`` feature, which would eliminate the high latency costs under
 which the 9p ``proxy`` backend currently suffers. However as of to date nobody
 has indicated plans for such kind of reimplementation unfortunately.
 
+RISC-V 'any' CPU type ``-cpu any`` (since 8.2)
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The 'any' CPU type was introduced back in 2018 and has been around since the
+initial RISC-V QEMU port. Its usage has always been unclear: users don't know
+what to expect from a CPU called 'any', and in fact the CPU does not do anything
+special that isn't already done by the default CPUs rv32/rv64.
+
+After the introduction of the 'max' CPU type, RISC-V now has a good coverage
+of generic CPUs: rv32 and rv64 as default CPUs and 'max' as a feature complete
+CPU for both 32 and 64 bit builds. Users are then discouraged to use the 'any'
+CPU type starting in 8.2.
 
 Block device options
 ''''''''''''''''''''

target/riscv/cpu.c

@@ -1522,6 +1522,11 @@ static void riscv_cpu_realize(DeviceState *dev, Error **errp)
     RISCVCPUClass *mcc = RISCV_CPU_GET_CLASS(dev);
     Error *local_err = NULL;
 
+    if (object_dynamic_cast(OBJECT(dev), TYPE_RISCV_CPU_ANY) != NULL) {
+        warn_report("The 'any' CPU is deprecated and will be "
+                    "removed in the future.");
+    }
+
     cpu_exec_realizefn(cs, &local_err);
     if (local_err != NULL) {
         error_propagate(errp, local_err);