[PULL 13/23] pc-bios/s390-ccw: Introduce virtio_tswap helpers

[Eric Farman <farman@linux.ibm.com>]

From: Zhuoying Cai <zycai@linux.ibm.com>

Replace the repeated pattern:

    be_ipl() ? x : bswapN(x)

with helpers that conditionally byte-swap based on the virtio transport
endianness.

While only the 16-bit helper is used immediately, the 32-bit and 64-bit
variants are added here for later use.

Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Reviewed-by: Jared Rossi <jrossi@linux.ibm.com>
Reviewed-by: Jason J. Herne <jjherne@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Link: https://lore.kernel.org/qemu-devel/20260924222949.147720-4-zycai@linux.ibm.com
Signed-off-by: Eric Farman <farman@linux.ibm.com>
---
 pc-bios/s390-ccw/virtio.c | 27 +++++++++++++++++++++------
 pc-bios/s390-ccw/virtio.h |  4 ++++
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
index 34c5e6ee22..8949e6c7c0 100644
--- a/pc-bios/s390-ccw/virtio.c
+++ b/pc-bios/s390-ccw/virtio.c
@@ -102,7 +102,7 @@ void vring_init(VRing *vr, VqInfo *info)
     vr->avail->idx = 0;
 
     /* We're running with interrupts off anyways, so don't bother */
-    vr->used->flags = be_ipl() ? VRING_USED_F_NO_NOTIFY : bswap16(VRING_USED_F_NO_NOTIFY);
+    vr->used->flags = virtio_tswap16(VRING_USED_F_NO_NOTIFY);
     vr->used->idx = 0;
     vr->used_idx = 0;
     vr->next_idx = 0;
@@ -143,6 +143,22 @@ bool be_ipl(void)
     }
 }
 
+/* Conditionally byte-swap between virtio-endian and s390x native big-endian. */
+uint16_t virtio_tswap16(uint16_t x)
+{
+    return be_ipl() ? x : bswap16(x);
+}
+
+uint32_t virtio_tswap32(uint32_t x)
+{
+    return be_ipl() ? x : bswap32(x);
+}
+
+uint64_t virtio_tswap64(uint64_t x)
+{
+    return be_ipl() ? x : bswap64(x);
+}
+
 /*
  * Format the virtio ring descriptor endianness
  * Return the available index increment in the appropriate endianness
@@ -159,12 +175,11 @@ void vring_send_buf(VRing *vr, void *p, int len, int flags)
 {
     uint16_t avail_idx;
 
-    avail_idx = be_ipl() ? vr->avail->idx : bswap16(vr->avail->idx);
+    avail_idx = virtio_tswap16(vr->avail->idx);
 
     /* For follow-up chains we need to keep the first entry point */
     if (!(flags & VRING_HIDDEN_IS_CHAIN)) {
-        vr->avail->ring[avail_idx % vr->num] = be_ipl() ? vr->next_idx :
-                                                          bswap16(vr->next_idx);
+        vr->avail->ring[avail_idx % vr->num] = virtio_tswap16(vr->next_idx);
     }
 
     vr->desc[vr->next_idx].addr = (unsigned long)p;
@@ -182,7 +197,7 @@ void vring_send_buf(VRing *vr, void *p, int len, int flags)
     /* Chains only have a single ID */
     if (!(flags & VRING_DESC_F_NEXT)) {
         avail_idx++;
-        vr->avail->idx = be_ipl() ? avail_idx : bswap16(avail_idx);
+        vr->avail->idx = virtio_tswap16(avail_idx);
     }
 }
 
@@ -190,7 +205,7 @@ int vr_poll(VRing *vr)
 {
     uint16_t used_idx;
 
-    used_idx = be_ipl() ? vr->used->idx : bswap16(vr->used->idx);
+    used_idx = virtio_tswap16(vr->used->idx);
     if (used_idx == vr->used_idx) {
         vring_notify(vr);
         yield();
diff --git a/pc-bios/s390-ccw/virtio.h b/pc-bios/s390-ccw/virtio.h
index aa307025e0..645dc288b1 100644
--- a/pc-bios/s390-ccw/virtio.h
+++ b/pc-bios/s390-ccw/virtio.h
@@ -287,6 +287,10 @@ int virtio_run(VDev *vdev, int vqid, VirtioCmd *cmd);
 int virtio_reset(VDev *vdev);
 int virtio_setup_ccw(VDev *vdev);
 
+uint16_t virtio_tswap16(uint16_t x);
+uint32_t virtio_tswap32(uint32_t x);
+uint64_t virtio_tswap64(uint64_t x);
+
 /* virtio-net.c */
 int virtio_net_init(void *mac_addr);
 void virtio_net_deinit(void);
-- 
2.55.0