[PATCH v2 1/6] pc-bios/s390-ccw: Refactor byte swapping

[jrossi@linux.ibm.com]

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

Introduce local variables to cache the byte-swapped values eliminating
some redundant byte swap operations.  Additionally, do byte swap when
polling to avoid a special case where endianness is preserved.

Reviewed-by: Eric Farman <farman@linux.ibm.com>
Signed-off-by: Zhuoying Cai <zycai@linux.ibm.com>
Signed-off-by: Jared Rossi <jrossi@linux.ibm.com>
---
 pc-bios/s390-ccw/virtio.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/pc-bios/s390-ccw/virtio.c b/pc-bios/s390-ccw/virtio.c
index 390b55c7b9..a448dc96e2 100644
--- a/pc-bios/s390-ccw/virtio.c
+++ b/pc-bios/s390-ccw/virtio.c
@@ -153,14 +153,14 @@ static void vr_bswap_descriptor(VRingDesc *desc)
 
 void vring_send_buf(VRing *vr, void *p, int len, int flags)
 {
-    if (!be_ipl()) {
-        vr->avail->idx = bswap16(vr->avail->idx);
-    }
+    uint16_t avail_idx;
+
+    avail_idx = be_ipl() ? vr->avail->idx : bswap16(vr->avail->idx);
 
     /* For follow-up chains we need to keep the first entry point */
     if (!(flags & VRING_HIDDEN_IS_CHAIN)) {
-        vr->avail->ring[vr->avail->idx % vr->num] = be_ipl() ? vr->next_idx :
-                                                               bswap16(vr->next_idx);
+        vr->avail->ring[avail_idx % vr->num] = be_ipl() ? vr->next_idx :
+                                                          bswap16(vr->next_idx);
     }
 
     vr->desc[vr->next_idx].addr = (unsigned long)p;
@@ -177,23 +177,23 @@ void vring_send_buf(VRing *vr, void *p, int len, int flags)
 
     /* Chains only have a single ID */
     if (!(flags & VRING_DESC_F_NEXT)) {
-        vr->avail->idx++;
-    }
-
-    if (!be_ipl()) {
-        vr->avail->idx = bswap16(vr->avail->idx);
+        avail_idx++;
+        vr->avail->idx = be_ipl() ? avail_idx : bswap16(avail_idx);
     }
 }
 
 int vr_poll(VRing *vr)
 {
-    if (vr->used->idx == vr->used_idx) {
+    uint16_t used_idx;
+
+    used_idx = be_ipl() ? vr->used->idx : bswap16(vr->used->idx);
+    if (used_idx == vr->used_idx) {
         vring_notify(vr);
         yield();
         return 0;
     }
 
-    vr->used_idx = vr->used->idx; /* Endianness is preserved */
+    vr->used_idx = used_idx;
     vr->next_idx = 0;
     vr->desc[0].len = 0;
     vr->desc[0].flags = 0;
-- 
2.54.0