From 33e60ff64a043b189d2661543b417b21b6f3667b Mon Sep 17 00:00:00 2001
From: Adam Judge <ajudge@iol.unh.edu>
Date: Tue, 9 Jun 2020 15:58:49 -0400
Subject: [PATCH] Prevent compiler from optimizing mmio_read64 to single 64b
 read

---
 nvme-print.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/nvme-print.c b/nvme-print.c
index fc8f99d..c0de928 100644
--- 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)
-- 
2.31.1