[PATCH v3] hw/misc/aspeed_scu: Handle AST2600 protection key registers correctly

[Tan Siewert]

The AST2600 SCU has two protection key registers (0x00 and 0x10) that
both need to be unlocked. (Un-)locking 0x00 modifies both protection key
registers, while modifying 0x10 only modifies itself.

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 <t...@siewert.io>
---
V3:
  - Change logic to unlock both registers on 0x00 write, while writing
    to 0x10 only modifies itself. [Jamin]

 hw/misc/aspeed_scu.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c
index 4930e00fed..993cb800a8 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,
@@ -730,15 +732,25 @@ 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__);
+        return;
     }
 
     trace_aspeed_scu_write(offset, size, data);
 
     switch (reg) {
     case AST2600_PROT_KEY:
-        s->regs[reg] = (data == ASPEED_SCU_PROT_KEY) ? 1 : 0;
+        /*
+         * Writing a value to SCU000 will modify both protection
+         * registers to each protection register individually.
+         */
+        u32 value = (data == ASPEED_SCU_PROT_KEY) ? 1 : 0;
+        s->regs[AST2600_PROT_KEY] = value;
+        s->regs[AST2600_PROT_KEY2] = value;
+        return;
+    case AST2600_PROT_KEY2:
+        s->regs[AST2600_PROT_KEY2] = (data == ASPEED_SCU_PROT_KEY) ? 1 : 0;
         return;
     case AST2600_HW_STRAP1:
     case AST2600_HW_STRAP2:
-- 
2.49.0