[Qemu-devel] [PATCH v1 21/22] RISC-V: No traps on writes to misa/minstret/mcycle

[Michael Clark]

These fields are marked WARL in the specification so illegal
writes are silently dropped.

Signed-off-by: Michael Clark <address@hidden>
Signed-off-by: Palmer Dabbelt <address@hidden>
---
 target/riscv/op_helper.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c
index aa101cc..f8595a6 100644
--- a/target/riscv/op_helper.c
+++ b/target/riscv/op_helper.c
@@ -200,17 +200,19 @@ void csr_write_helper(CPURISCVState *env, target_ulong 
val_to_write,
         break;
     }
     case CSR_MINSTRET:
-        qemu_log_mask(LOG_UNIMP, "CSR_MINSTRET: write not implemented");
-        goto do_illegal;
+        /* minstret is WARL so unsupported writes are ignored */
+        break;
     case CSR_MCYCLE:
-        qemu_log_mask(LOG_UNIMP, "CSR_MCYCLE: write not implemented");
-        goto do_illegal;
+        /* mcycle is WARL so unsupported writes are ignored */
+        break;
+#if defined(TARGET_RISCV32)
     case CSR_MINSTRETH:
-        qemu_log_mask(LOG_UNIMP, "CSR_MINSTRETH: write not implemented");
-        goto do_illegal;
+        /* minstreth is WARL so unsupported writes are ignored */
+        break;
     case CSR_MCYCLEH:
-        qemu_log_mask(LOG_UNIMP, "CSR_MCYCLEH: write not implemented");
-        goto do_illegal;
+        /* mcycleh is WARL so unsupported writes are ignored */
+        break;
+#endif
     case CSR_MUCOUNTEREN:
         env->mucounteren = val_to_write;
         break;
@@ -300,10 +302,9 @@ void csr_write_helper(CPURISCVState *env, target_ulong 
val_to_write,
     case CSR_MBADADDR:
         env->mbadaddr = val_to_write;
         break;
-    case CSR_MISA: {
-        qemu_log_mask(LOG_UNIMP, "CSR_MISA: misa writes not supported");
-        goto do_illegal;
-    }
+    case CSR_MISA:
+        /* misa is WARL so unsupported writes are ignored */
+        break;
     case CSR_PMPCFG0:
     case CSR_PMPCFG1:
     case CSR_PMPCFG2:
@@ -328,7 +329,6 @@ void csr_write_helper(CPURISCVState *env, target_ulong 
val_to_write,
     case CSR_PMPADDR15:
        pmpaddr_csr_write(env, csrno - CSR_PMPADDR0, val_to_write);
        break;
-    do_illegal:
 #endif
     default:
         do_raise_exception_err(env, RISCV_EXCP_ILLEGAL_INST, GETPC());
-- 
2.7.0