[RFC PATCH v2 2/3] hw/intc: Support 32/64-bit mtimecmp and mtime accesses in RISC-V ACLINT

[frank . chang]

From: Frank Chang <frank.chang@sifive.com>

RISC-V privilege spec defines that:

* In RV32, memory-mapped writes to mtimecmp modify only one 32-bit part
  of the register.
* For RV64, naturally aligned 64-bit memory accesses to the mtime and
  mtimecmp registers are additionally supported and are atomic.

It's possible to perform both 32/64-bit read/write accesses to both
mtimecmp and mtime registers.

Signed-off-by: Frank Chang <frank.chang@sifive.com>
---
 hw/intc/riscv_aclint.c | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/hw/intc/riscv_aclint.c b/hw/intc/riscv_aclint.c
index 3b598d8a7e..e7b103e83a 100644
--- a/hw/intc/riscv_aclint.c
+++ b/hw/intc/riscv_aclint.c
@@ -126,9 +126,9 @@ static uint64_t riscv_aclint_mtimer_read(void *opaque, 
hwaddr addr,
             qemu_log_mask(LOG_GUEST_ERROR,
                           "aclint-mtimer: invalid hartid: %zu", hartid);
         } else if ((addr & 0x7) == 0) {
-            /* timecmp_lo */
+            /* timecmp_lo for RV32/RV64 or timecmp for RV64 */
             uint64_t timecmp = env->timecmp;
-            return timecmp & 0xFFFFFFFF;
+            return (size == 4) ? (timecmp & 0xFFFFFFFF) : timecmp;
         } else if ((addr & 0x7) == 4) {
             /* timecmp_hi */
             uint64_t timecmp = env->timecmp;
@@ -139,8 +139,9 @@ static uint64_t riscv_aclint_mtimer_read(void *opaque, 
hwaddr addr,
             return 0;
         }
     } else if (addr == mtimer->time_base) {
-        /* time_lo */
-        return cpu_riscv_read_rtc(mtimer->timebase_freq) & 0xFFFFFFFF;
+        /* time_lo for RV32/RV64 or timecmp for RV64 */
+        uint64_t rtc = cpu_riscv_read_rtc(mtimer->timebase_freq);
+        return (size == 4) ? (rtc & 0xFFFFFFFF) : rtc;
     } else if (addr == mtimer->time_base + 4) {
         /* time_hi */
         return (cpu_riscv_read_rtc(mtimer->timebase_freq) >> 32) & 0xFFFFFFFF;
@@ -167,12 +168,17 @@ static void riscv_aclint_mtimer_write(void *opaque, 
hwaddr addr,
             qemu_log_mask(LOG_GUEST_ERROR,
                           "aclint-mtimer: invalid hartid: %zu", hartid);
         } else if ((addr & 0x7) == 0) {
-            /* timecmp_lo */
-            uint64_t timecmp_hi = env->timecmp >> 32;
-            riscv_aclint_mtimer_write_timecmp(mtimer, RISCV_CPU(cpu), hartid,
-                timecmp_hi << 32 | (value & 0xFFFFFFFF),
-                mtimer->timebase_freq);
-            return;
+            if (size == 4) {
+                /* timecmp_lo for RV32/RV64 */
+                uint64_t timecmp_hi = env->timecmp >> 32;
+                riscv_aclint_mtimer_write_timecmp(mtimer, RISCV_CPU(cpu), 
hartid,
+                    timecmp_hi << 32 | (value & 0xFFFFFFFF),
+                    mtimer->timebase_freq);
+            } else {
+                /* timecmp for RV64 */
+                riscv_aclint_mtimer_write_timecmp(mtimer, RISCV_CPU(cpu), 
hartid,
+                                                  value, 
mtimer->timebase_freq);
+            }
         } else if ((addr & 0x7) == 4) {
             /* timecmp_hi */
             uint64_t timecmp_lo = env->timecmp;
-- 
2.31.1