virtio_legacy_get_byteswap: endian-ambivalent targets using legacy virtio

virtio data structures are defined as "target endian", which assumes
that's a fixed value.  In fact, that actually means it's platform-specific.
The OASIS virtio 1.0 spec will fix this, by making all little endian.

We need to support both implementations and we want to share as much code
as possible.

A good way to do it is to introduce a per-device boolean property to tell
memory accessors whether they should swap bytes or not. This flag should
be set at device reset time, because:
- endianness won't change while the device is in use, and if we reboot
  into a different endianness, a new device reset will occur
- as suggested by Alexander Graf, we can keep all the logic to set the
  property in a single place and share all the virtio memory accessors
  between the two implementations

For legacy devices, we rely on a per-platform hook to set the flag. The
virtio 1.0 implementation will just have to add some more logic in
virtio_reset() instead of calling the hook:

if (vdev->legacy) {
   vdev->needs_byteswap = virtio_legacy_get_byteswap();
} else {
#ifdef HOST_WORDS_BIGENDIAN
   vdev->needs_byteswap = true;
#else
   vdev->needs_byteswap = false;
#endif
}

The needs_byteswap flag is preserved accross migrations.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[ fixed checkpatch.pl error with the virtio_byteswap initialisation,
  ldq_phys() API change,
  relicensed virtio-access.h to GPLv2+ on Rusty's request,
  introduce a per-device needs_byteswap flag,
  add VirtIODevice * arg to virtio helpers,
  rename virtio_get_byteswap to virtio_legacy_get_byteswap,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio: allow byte swapping for vring and config access

This is based on a simpler patch by Anthony Liguouri, which only handled
the vring accesses.  We also need some drivers to access these helpers,
eg. for data which contains headers.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
[ ldq_phys() API change,
  use per-device needs_byteswap flag,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-net: use virtio wrappers to access headers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ use per-device needs_byteswap flag,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-balloon: use virtio wrappers to access page frame numbers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ use per-device needs_byteswap flag,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-blk: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ use per-device needs_byteswap flag,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-scsi: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ use per-device needs_byteswap flag,
  fix missing tswap32 in virtio_scsi_push_event(),
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-serial-bus: use virtio wrappers to access headers

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reviewed-by: Anthony Liguori <aliguori@us.ibm.com>
[ use per-device needs_byteswap flag,
  Greg Kurz <gkurz@linux.vnet.ibm.com> ]
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
virtio-9p: use virtio wrappers to access headers

Note that st*_raw and ld*_raw are effectively replaced by st*_p and ld*_p.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
target-ppc: ppc64 target's virtio can be either endian

We base it on the OS endian, as reflected by the endianness of the
interrupt vectors (handled through the ILE bit in the LPCR register).

Using first_cpu to fetch the registers from KVM may look arbitrary
and awkward, but it is okay because KVM sets/unsets the ILE bit on
all CPUs.

Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Reviewed-by: Alexander Graf <agraf@suse.de>