hw/nvram/aspeed_otp: Add 'drive' property to support block backend

This patch introduces a 'drive' property to the Aspeed OTP device,
allowing it to be backed by a block device. Users can now preload
OTP data via QEMU CLI using a block backend.

Example usage:
  ./qemu-system-arm \
    -blockdev driver=file,filename=otpmem.img,node-name=otp \
    -global aspeed-otp.drive=otp \
    ...

If the drive is provided, its content will be loaded as the initial OTP
state. Otherwise, an internal memory buffer will be used.

Signed-off-by: Kane-Chen-AS <kane_chen@aspeedtech.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20250812094011.2617526-5-kane_chen@aspeedtech.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

hw/nvram/aspeed_otp.c

@@ -35,13 +35,25 @@ static bool aspeed_otp_init_storage(AspeedOTPState *s, Error **errp)
 {
     uint32_t *p;
     int i, num;
+    uint64_t perm;
 
+    if (s->blk) {
+        perm = BLK_PERM_CONSISTENT_READ |
+               (blk_supports_write_perm(s->blk) ? BLK_PERM_WRITE : 0);
+        if (blk_set_perm(s->blk, perm, BLK_PERM_ALL, errp) < 0) {
+            return false;
+        }
+        if (blk_pread(s->blk, 0, s->size, s->storage, 0) < 0) {
+            error_setg(errp, "Failed to read the initial flash content");
+            return false;
+        }
+    } else {
         num = s->size / sizeof(uint32_t);
         p = (uint32_t *)s->storage;
         for (i = 0; i < num; i++) {
             p[i] = (i % 2 == 0) ? 0x00000000 : 0xFFFFFFFF;
         }
-
+    }
     return true;
 }
 
@@ -75,6 +87,7 @@ static void aspeed_otp_realize(DeviceState *dev, Error **errp)
 
 static const Property aspeed_otp_properties[] = {
     DEFINE_PROP_UINT64("size", AspeedOTPState, size, 0),
+    DEFINE_PROP_DRIVE("drive", AspeedOTPState, blk),
 };
 
 static void aspeed_otp_class_init(ObjectClass *klass, const void *data)