hw: timer: ibex_timer: update/add reg address

The following changes:
1. Fixes the incorrectly set CTRL register address. As
per [1] https://docs.opentitan.org/hw/ip/rv_timer/doc/#register-table

The CTRL register is @ 0x04.

This was found when attempting to fixup a bug where a timer_interrupt
was not serviced on TockOS-OpenTitan.

2. Adds ALERT_TEST register as documented on [1], adding repective
   switch cases to error handle and later implement functionality.

Signed-off-by: Wilfred Mallawa <wilfred.mallawa@wdc.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Tested-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Message-id: 20220111071025.4169189-2-alistair.francis@opensource.wdc.com
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

hw/timer/ibex_timer.c

@@ -34,7 +34,9 @@
 #include "target/riscv/cpu.h"
 #include "migration/vmstate.h"
 
-REG32(CTRL, 0x00)
+REG32(ALERT_TEST, 0x00)
+    FIELD(ALERT_TEST, FATAL_FAULT, 0, 1)
+REG32(CTRL, 0x04)
     FIELD(CTRL, ACTIVE, 0, 1)
 REG32(CFG0, 0x100)
     FIELD(CFG0, PRESCALE, 0, 12)
@@ -142,6 +144,10 @@ static uint64_t ibex_timer_read(void *opaque, hwaddr addr,
     uint64_t retvalue = 0;
 
     switch (addr >> 2) {
+    case R_ALERT_TEST:
+        qemu_log_mask(LOG_GUEST_ERROR,
+                        "Attempted to read ALERT_TEST, a write only register");
+        break;
     case R_CTRL:
         retvalue = s->timer_ctrl;
         break;
@@ -186,6 +192,9 @@ static void ibex_timer_write(void *opaque, hwaddr addr,
     uint32_t val = val64;
 
     switch (addr >> 2) {
+    case R_ALERT_TEST:
+        qemu_log_mask(LOG_UNIMP, "Alert triggering not supported");
+        break;
     case R_CTRL:
         s->timer_ctrl = val;
         break;