On 07/01/2016 12:32, Greg Kurz wrote:
> When adding cross-endian support, we introduced the TARGET_IS_BIENDIAN macro
> and the virtio_access_is_big_endian() helper to have a branchless fast path
> in the virtio memory accessors for targets that don't switch endian.
>
> This was considered as a strong requirement at the time.
>
> Now we have added a runtime check for virtio 1.0, which ruins the benefit
> of the virtio_access_is_big_endian() helper for always little-endian targets.
>
> With this patch, always little-endian targets stop checking for virtio 1.0,
> since the result is little-endian in all cases.
>
> Signed-off-by: Greg Kurz <gk...@linux.vnet.ibm.com>
> ---
> include/hw/virtio/virtio-access.h | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/include/hw/virtio/virtio-access.h
> b/include/hw/virtio/virtio-access.h
> index f1f12afe9089..fba4b4a4e1b2 100644
> --- a/include/hw/virtio/virtio-access.h
> +++ b/include/hw/virtio/virtio-access.h
> @@ -19,10 +19,13 @@
>
> static inline bool virtio_access_is_big_endian(VirtIODevice *vdev)
> {
> +#if defined(TARGET_IS_BIENDIAN) || defined(TARGET_WORDS_BIGENDIAN)
> if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) {
> /* Devices conforming to VIRTIO 1.0 or later are always LE. */
> return false;
> }
> +#endif
virtio_is_big_endian() checks VIRTIO_F_VERSION_1, so you don't need to
check it here if TARGET_IS_BIENDIAN is defined.
> +
> #if defined(TARGET_IS_BIENDIAN)
> return virtio_is_big_endian(vdev);
> #elif defined(TARGET_WORDS_BIGENDIAN)
>
>
So you can move virtio_vdev_has_feature() here.
Laurent
