[xen staging] xen/dt: Remove loop in dt_read_number()

[patchbot@xxxxxxx]

commit c65ff27d7158ca31cca0bb4b77a515c8a5bddced
Author:     Alejandro Vallejo <agarciav@xxxxxxx>
AuthorDate: Thu Jun 19 13:42:04 2025 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Fri Jun 20 17:47:31 2025 -0700

    xen/dt: Remove loop in dt_read_number()
    
    The DT spec declares only two number types for a property: u32 and u64,
    as per Table 2.3 in Section 2.2.4. Remove unbounded loop and replace
    with a switch statement. Default to a size of 1 cell in the nonsensical
    size case, with a warning printed on the Xen console.
    
    Suggested-by: Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Alejandro Vallejo <agarciav@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/include/xen/device_tree.h | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index 75017e4266..d2de7c3a13 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -261,10 +261,22 @@ void intc_dt_preinit(void);
 /* Helper to read a big number; size is in cells (not bytes) */
 static inline u64 dt_read_number(const __be32 *cell, int size)
 {
-    u64 r = 0;
+    u64 r = be32_to_cpu(*cell);
+
+    switch ( size )
+    {
+    case 1:
+        break;
+    case 2:
+        r = (r << 32) | be32_to_cpu(cell[1]);
+        break;
+    default:
+        /* Nonsensical size. default to 1 */
+        printk(XENLOG_ERR "dt_read_number(,%d) bad size\n", size);
+        ASSERT_UNREACHABLE();
+        break;
+    };
 
-    while ( size-- )
-        r = (r << 32) | be32_to_cpu(*(cell++));
     return r;
 }
 
--
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