Thanks to previous refactoring, we can see more easily it is strictly
equivalent to always call virtio_vdev_is_big_endian.

static inline bool virtio_vdev_is_big_endian(VirtIODevice *vdev)
{
    if (virtio_vdev_is_legacy(vdev)) {
        assert(vdev->device_endian != VIRTIO_DEVICE_ENDIAN_UNKNOWN);
        return vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG;
    }
    /* Devices conforming to VIRTIO 1.0 or later are always LE. */
    return false;
}

The key is to understand that vdev->device_endian is initialized as
expected. It always contains cpu endianness, and not
device endianness, ignoring if device is legacy or not.

By default, it's initialized to vdev->device_endian =
virtio_default_endian(), which matches target default endianness.
Then, on virtio_reset, it will be initialized with current_cpu
endianness (if there is one current_cpu).

void virtio_reset() {
    ...
    if (current_cpu) {
        /* Guest initiated reset */
        vdev->device_endian = virtio_current_cpu_endian();
    } else {
        /* System reset */
        vdev->device_endian = virtio_default_endian();
    }

Now, we can see how existing virtio_access_is_big_endian is equivalent
to virtio_vdev_is_big_endian. Let's break the existing function in its 3
variants, and compare that to virtio_vdev_is_big_endian.

static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
- #if defined(LEGACY_VIRTIO_IS_BIENDIAN)
    return virtio_vdev_is_big_endian(vdev);
  This is the exact replacement we did, so equivalent.
- #elif TARGET_BIG_ENDIAN
    if (virtio_vdev_is_modern(vdev)) {
        return false;
    }
    return true;

  we know target_is_big_endian(), so
  vdev->device_endian == VIRTIO_DEVICE_ENDIAN_BIG.
  if (virtio_vdev_is_legacy(vdev)) {
      return VIRTIO_DEVICE_ENDIAN_BIG == VIRTIO_DEVICE_ENDIAN_BIG;
  }
  return false;
  It's written in opposite style compared to existing code (if legacy vs
  if modern), but it's strictly equivalent.
- #else
    return false;
  we know !target_is_big_endian(), so
  vdev->device_endian == VIRTIO_DEVICE_ENDIAN_LITTLE.
  if virtio_vdev_is_legacy(vdev) {
    return VIRTIO_DEVICE_ENDIAN_LITTLE == VIRTIO_DEVICE_ENDIAN_BIG;
  }
  return false;
  So it always return false, as expected.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
---
 include/hw/virtio/virtio-access.h | 42 +++++++++----------------------
 hw/virtio/virtio.c                |  4 +--
 2 files changed, 14 insertions(+), 32 deletions(-)

diff --git a/include/hw/virtio/virtio-access.h b/include/hw/virtio/virtio-access.h
index 0c5514178e4..506be642c9f 100644
--- a/include/hw/virtio/virtio-access.h
+++ b/include/hw/virtio/virtio-access.h
@@ -21,27 +21,9 @@
 #include "hw/virtio/virtio.h"
 #include "hw/virtio/virtio-bus.h"
 
-#if defined(TARGET_PPC64) || defined(TARGET_ARM)
-#define LEGACY_VIRTIO_IS_BIENDIAN 1
-#endif
-
-static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
-{
-#if defined(LEGACY_VIRTIO_IS_BIENDIAN)
-    return virtio_vdev_is_big_endian(vdev);
-#elif TARGET_BIG_ENDIAN
-    if (virtio_vdev_is_modern(vdev)) {
-        return false;
-    }
-    return true;
-#else
-    return false;
-#endif
-}
-
 static inline void virtio_stw_p(VirtIODevice *vdev, void *ptr, uint16_t v)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         stw_be_p(ptr, v);
     } else {
         stw_le_p(ptr, v);
@@ -50,7 +32,7 @@ static inline void virtio_stw_p(VirtIODevice *vdev, void *ptr, uint16_t v)
 
 static inline void virtio_stl_p(VirtIODevice *vdev, void *ptr, uint32_t v)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         stl_be_p(ptr, v);
     } else {
         stl_le_p(ptr, v);
@@ -59,7 +41,7 @@ static inline void virtio_stl_p(VirtIODevice *vdev, void *ptr, uint32_t v)
 
 static inline void virtio_stq_p(VirtIODevice *vdev, void *ptr, uint64_t v)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         stq_be_p(ptr, v);
     } else {
         stq_le_p(ptr, v);
@@ -68,7 +50,7 @@ static inline void virtio_stq_p(VirtIODevice *vdev, void *ptr, uint64_t v)
 
 static inline int virtio_lduw_p(VirtIODevice *vdev, const void *ptr)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         return lduw_be_p(ptr);
     } else {
         return lduw_le_p(ptr);
@@ -77,7 +59,7 @@ static inline int virtio_lduw_p(VirtIODevice *vdev, const void *ptr)
 
 static inline int virtio_ldl_p(VirtIODevice *vdev, const void *ptr)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         return ldl_be_p(ptr);
     } else {
         return ldl_le_p(ptr);
@@ -86,7 +68,7 @@ static inline int virtio_ldl_p(VirtIODevice *vdev, const void *ptr)
 
 static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, const void *ptr)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         return ldq_be_p(ptr);
     } else {
         return ldq_le_p(ptr);
@@ -96,9 +78,9 @@ static inline uint64_t virtio_ldq_p(VirtIODevice *vdev, const void *ptr)
 static inline uint16_t virtio_tswap16(VirtIODevice *vdev, uint16_t s)
 {
 #if HOST_BIG_ENDIAN
-    return virtio_access_is_big_endian(vdev) ? s : bswap16(s);
+    return virtio_vdev_is_big_endian(vdev) ? s : bswap16(s);
 #else
-    return virtio_access_is_big_endian(vdev) ? bswap16(s) : s;
+    return virtio_vdev_is_big_endian(vdev) ? bswap16(s) : s;
 #endif
 }
 
@@ -110,9 +92,9 @@ static inline void virtio_tswap16s(VirtIODevice *vdev, uint16_t *s)
 static inline uint32_t virtio_tswap32(VirtIODevice *vdev, uint32_t s)
 {
 #if HOST_BIG_ENDIAN
-    return virtio_access_is_big_endian(vdev) ? s : bswap32(s);
+    return virtio_vdev_is_big_endian(vdev) ? s : bswap32(s);
 #else
-    return virtio_access_is_big_endian(vdev) ? bswap32(s) : s;
+    return virtio_vdev_is_big_endian(vdev) ? bswap32(s) : s;
 #endif
 }
 
@@ -124,9 +106,9 @@ static inline void virtio_tswap32s(VirtIODevice *vdev, uint32_t *s)
 static inline uint64_t virtio_tswap64(VirtIODevice *vdev, uint64_t s)
 {
 #if HOST_BIG_ENDIAN
-    return virtio_access_is_big_endian(vdev) ? s : bswap64(s);
+    return virtio_vdev_is_big_endian(vdev) ? s : bswap64(s);
 #else
-    return virtio_access_is_big_endian(vdev) ? bswap64(s) : s;
+    return virtio_vdev_is_big_endian(vdev) ? bswap64(s) : s;
 #endif
 }
 
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index b0987e66d5b..2ae238001dc 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -222,7 +222,7 @@ static inline uint16_t virtio_lduw_phys_cached(VirtIODevice *vdev,
                                                MemoryRegionCache *cache,
                                                hwaddr pa)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         return lduw_be_phys_cached(cache, pa);
     }
     return lduw_le_phys_cached(cache, pa);
@@ -232,7 +232,7 @@ static inline void virtio_stw_phys_cached(VirtIODevice *vdev,
                                           MemoryRegionCache *cache,
                                           hwaddr pa, uint16_t value)
 {
-    if (virtio_access_is_big_endian(vdev)) {
+    if (virtio_vdev_is_big_endian(vdev)) {
         stw_be_phys_cached(cache, pa, value);
     } else {
         stw_le_phys_cached(cache, pa, value);
-- 
2.47.3

On 13/2/26 00:46, Pierrick Bouvier wrote:
> Thanks to previous refactoring, we can see more easily it is strictly
> equivalent to always call virtio_vdev_is_big_endian.


> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>   include/hw/virtio/virtio-access.h | 42 +++++++++----------------------
>   hw/virtio/virtio.c                |  4 +--
>   2 files changed, 14 insertions(+), 32 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>