memory: Introduce DEVICE_HOST_ENDIAN for ram device

At the moment ram device's memory regions are DEVICE_NATIVE_ENDIAN. It's
incorrect. This memory region is backed by a MMIO area in host, so the
uint64_t data that MemoryRegionOps read from/write to this area should be
host-endian rather than target-endian. Hence, current code does not work
when target and host endianness are different which is the most common case
on PPC64. To fix it, this introduces DEVICE_HOST_ENDIAN for the ram device.

This has been tested on PPC64 BE/LE host/guest in all possible combinations
including TCG.
Suggested-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NYongji Xie <xyjxie@linux.vnet.ibm.com>
Message-Id: <1488171164-28319-1-git-send-email-xyjxie@linux.vnet.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

include/exec/cpu-common.h

@@ -36,6 +36,12 @@ enum device_endian {
     DEVICE_LITTLE_ENDIAN,
 };
 
+#if defined(HOST_WORDS_BIGENDIAN)
+#define DEVICE_HOST_ENDIAN DEVICE_BIG_ENDIAN
+#else
+#define DEVICE_HOST_ENDIAN DEVICE_LITTLE_ENDIAN
+#endif
+
 /* address in the RAM (different from a physical address) */
 #if defined(CONFIG_XEN_BACKEND)
 typedef uint64_t ram_addr_t;

memory.c

@@ -1182,7 +1182,7 @@ static void memory_region_ram_device_write(void *opaque, hwaddr addr,
 static const MemoryRegionOps ram_device_mem_ops = {
     .read = memory_region_ram_device_read,
     .write = memory_region_ram_device_write,
-    .endianness = DEVICE_NATIVE_ENDIAN,
+    .endianness = DEVICE_HOST_ENDIAN,
     .valid = {
         .min_access_size = 1,
         .max_access_size = 8,