qemu riscv, thead c906, Linux boot regression

[Björn Töpel]

Hi!

I bumped the RISC-V Linux kernel CI to use qemu 8.2.0, and realized that
thead c906 didn't boot anymore. Bisection points to commit d6a427e2c0b2
("target/riscv/cpu.c: restrict 'marchid' value")

Reverting that commit, or the hack below solves the boot issue:

--8<--
diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
index 8cbfc7e781ad..e18596c8a55a 100644
--- a/target/riscv/cpu.c
+++ b/target/riscv/cpu.c
@@ -505,6 +505,9 @@ static void rv64_thead_c906_cpu_init(Object *obj)
     cpu->cfg.ext_xtheadsync = true;
 
     cpu->cfg.mvendorid = THEAD_VENDOR_ID;
+    cpu->cfg.marchid = ((QEMU_VERSION_MAJOR << 16) |
+                        (QEMU_VERSION_MINOR << 8)  |
+                        (QEMU_VERSION_MICRO));
 #ifndef CONFIG_USER_ONLY
     set_satp_mode_max_supported(cpu, VM_1_10_SV39);
 #endif
--8<--

I'm unsure what the correct qemu way of adding a default value is,
or if c906 should have a proper marchid.

Maybe Christoph or Zhiwei can answer?

qemu command-line:
qemu-system-riscv64 -nodefaults -nographic -machine virt,acpi=off \
   -cpu thead-c906 ...


Thanks,
Björn