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

[Alejandro Vallejo <agarciav@xxxxxxx>]

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>
---
Based on this suggestion by Daniel:

    
https://lore.kernel.org/xen-devel/a66c11c4-cfac-4934-b1f5-e07c728db8de@xxxxxxxxxxxxxxxxxxxx/

I'd be happier panicking there, seeing how DTs are by their very nature
trusted blobs. But I suspect defaulting to something will find less
resistance in review. I don't care much either way.
---
 xen/include/xen/device_tree.h | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/xen/include/xen/device_tree.h b/xen/include/xen/device_tree.h
index 75017e4266..2daef8659e 100644
--- a/xen/include/xen/device_tree.h
+++ b/xen/include/xen/device_tree.h
@@ -261,10 +261,19 @@ 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]);
+    default:
+        // Nonsensical size. default to 1.
+        printk(XENLOG_WARNING "dt_read_number(%d) bad size", size);
+    };
 
-    while ( size-- )
-        r = (r << 32) | be32_to_cpu(*(cell++));
     return r;
 }
 

base-commit: 14c57887f36937c1deb9eeca852c3a7595d2d0b8
-- 
2.43.0