[RFC PATCH 06/11] target/riscv: Update CSR xtvec in CLIC mode

[LIU Zhiwei <zhiwei_liu@c-sky.com>]

The new CLIC interrupt-handling mode is encoded as a new state in the
existing WARL xtvec register, where the low two bits of are 11.

Signed-off-by: LIU Zhiwei <zhiwei_liu@c-sky.com>
---
 target/riscv/csr.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index f6c84b9fe4..39ff72041a 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -637,9 +637,18 @@ static int read_mtvec(CPURISCVState *env, int csrno, target_ulong *val)
 
 static int write_mtvec(CPURISCVState *env, int csrno, target_ulong val)
 {
-    /* bits [1:0] encode mode; 0 = direct, 1 = vectored, 2 >= reserved */
+    /*
+     * bits [1:0] encode mode; 0 = direct, 1 = vectored, 3 = CLIC,
+     * others reserved
+     */
     if ((val & 3) < 2) {
         env->mtvec = val;
+    } else if ((val & 1) && env->clic) {
+        /*
+         * If only CLIC mode is supported, writes to bit 1 are also ignored and
+         * it is always set to one. CLIC mode hardwires xtvec bits 2-5 to zero.
+         */
+        env->mtvec = ((val & ~0x3f) << 6) | (0b000011);
     } else {
         qemu_log_mask(LOG_UNIMP, "CSR_MTVEC: reserved mode not supported\n");
     }
@@ -837,9 +846,18 @@ static int read_stvec(CPURISCVState *env, int csrno, target_ulong *val)
 
 static int write_stvec(CPURISCVState *env, int csrno, target_ulong val)
 {
-    /* bits [1:0] encode mode; 0 = direct, 1 = vectored, 2 >= reserved */
+    /*
+     * bits [1:0] encode mode; 0 = direct, 1 = vectored, 3 = CLIC,
+     * others reserved
+     */
     if ((val & 3) < 2) {
         env->stvec = val;
+    } else if ((val & 1) && env->clic) {
+        /*
+         * If only CLIC mode is supported, writes to bit 1 are also ignored and
+         * it is always set to one. CLIC mode hardwires xtvec bits 2-5 to zero.
+         */
+        env->stvec = ((val & ~0x3f) << 6) | (0b000011);
     } else {
         qemu_log_mask(LOG_UNIMP, "CSR_STVEC: reserved mode not supported\n");
     }
-- 
2.25.1