Prevent compiler from optimizing mmio_read64 to single 64b read

linux-nvme · Jun 18, 2020 · 33e60ff · 33e60ff
1 parent b918bc7
commit 33e60ff
Showing 1 changed file with 6 additions and 2 deletions.
diff --git a/nvme-print.c b/nvme-print.c
@@ -1311,9 +1311,13 @@ static inline uint32_t mmio_read32(void *addr)
 /* Access 64-bit registers as 2 32-bit; Some devices fail 64-bit MMIO. */
 static inline __u64 mmio_read64(void *addr)
 {
-	__le32 *p = addr;
+	const volatile __u32 *p = addr;
+	__u32 low, high;
+
+	low = le32_to_cpu(*p);
+	high = le32_to_cpu(*(p + 1));
 
-	return le32_to_cpu(*p) | ((uint64_t)le32_to_cpu(*(p + 1)) << 32);
+	return ((__u64) high << 32) | low;
 }
 
 static void json_ctrl_registers(void *bar)