[PATCH] hw/misc/aspeed_scu: Handle AST2600 protection key registers correctly

[Tan Siewert <tan@siewert.io>]

The AST2600 SCU has two protection key registers (0x00 and 0x10) that
both need to be unlocked. Each must be unlocked individually, but
locking one will lock both.

This commit updates the SCU write logic to reject writes unless both
protection key registers are unlocked, matching the behaviour of
real hardware.

Signed-off-by: Tan Siewert <tan@siewert.io>
---
 hw/misc/aspeed_scu.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c
index 4930e00fed..8e9eac4629 100644
--- a/hw/misc/aspeed_scu.c
+++ b/hw/misc/aspeed_scu.c
@@ -91,6 +91,7 @@
 #define BMC_DEV_ID           TO_REG(0x1A4)
 
 #define AST2600_PROT_KEY          TO_REG(0x00)
+#define AST2600_PROT_KEY2         TO_REG(0x10)
 #define AST2600_SILICON_REV       TO_REG(0x04)
 #define AST2600_SILICON_REV2      TO_REG(0x14)
 #define AST2600_SYS_RST_CTRL      TO_REG(0x40)
@@ -722,6 +723,7 @@ static void aspeed_ast2600_scu_write(void *opaque, hwaddr offset,
     int reg = TO_REG(offset);
     /* Truncate here so bitwise operations below behave as expected */
     uint32_t data = data64;
+    bool unlocked = s->regs[AST2600_PROT_KEY] && s->regs[AST2600_PROT_KEY2];
 
     if (reg >= ASPEED_AST2600_SCU_NR_REGS) {
         qemu_log_mask(LOG_GUEST_ERROR,
@@ -730,7 +732,7 @@ static void aspeed_ast2600_scu_write(void *opaque, hwaddr offset,
         return;
     }
 
-    if (reg > PROT_KEY && !s->regs[PROT_KEY]) {
+    if ((reg != AST2600_PROT_KEY && reg != AST2600_PROT_KEY2) && !unlocked) {
         qemu_log_mask(LOG_GUEST_ERROR, "%s: SCU is locked!\n", __func__);
     }
 
@@ -738,7 +740,18 @@ static void aspeed_ast2600_scu_write(void *opaque, hwaddr offset,
 
     switch (reg) {
     case AST2600_PROT_KEY:
-        s->regs[reg] = (data == ASPEED_SCU_PROT_KEY) ? 1 : 0;
+    case AST2600_PROT_KEY2:
+        /*
+         * Writing a value other than the protection key will lock
+         * both protection registers, but unlocking must be done
+         * to each protection register individually.
+         */
+        if (data != ASPEED_SCU_PROT_KEY) {
+            s->regs[AST2600_PROT_KEY] = 0;
+            s->regs[AST2600_PROT_KEY2] = 0;
+        } else {
+            s->regs[reg] = (data == ASPEED_SCU_PROT_KEY) ? 1 : 0;
+        }
         return;
     case AST2600_HW_STRAP1:
     case AST2600_HW_STRAP2:
-- 
2.49.0