Fix merge of bounce buffer segments in amd64 bus dma.

If the physical pages are contiguous, _bus_dmamap_load_buffer()
tries to merge the segments.  In case of mbuf chains, it can happen
that the physical bounce buffers are contiguous, but the virtual
addresses of mbuf m_data are not.  Then during transmit _bus_dmamap_sync()
tries to copy segments where it cannot access the virtual source
address which is mapped in a different mbuf.  So if bounce buffers
are used, physical and virtual buffer must be contigous, to merge
a segment.
While there, split check and decrement of variable i in a for loop
to make the code readable.

with and OK hshoexer@

diff --git a/sys/arch/amd64/amd64/bus_dma.c b/sys/arch/amd64/amd64/bus_dma.c
index c29501a..070c342 100644 (file)
--- a/sys/arch/amd64/amd64/bus_dma.c
+++ b/sys/arch/amd64/amd64/bus_dma.c
@@ -1,4 +1,4 @@
-/*     $OpenBSD: bus_dma.c,v 1.56 2024/08/20 15:30:29 bluhm Exp $      */
+/*     $OpenBSD: bus_dma.c,v 1.57 2024/08/22 11:36:24 bluhm Exp $      */
 /*     $NetBSD: bus_dma.c,v 1.3 2003/05/07 21:33:58 fvdl Exp $ */
 
 /*-
@@ -499,7 +499,7 @@ _bus_dmamap_sync(bus_dma_tag_t t, bus_dmamap_t map, bus_addr_t addr,
        if (!use_bounce_buffer)
                return;
 
-       for (i = map->_dm_segcnt, sg = map->dm_segs; size && i--; sg++) {
+       for (i = map->_dm_segcnt, sg = map->dm_segs; size && i; i--, sg++) {
                if (off >= sg->ds_len) {
                        off -= sg->ds_len;
                        continue;
@@ -767,9 +767,11 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map, void *buf,
                             map->_dm_maxsegsz &&
                            (map->_dm_boundary == 0 ||
                             (map->dm_segs[seg].ds_addr & bmask) ==
-                            (curaddr & bmask)))
+                            (curaddr & bmask)) &&
+                           (!use_bounce_buffer || (map->dm_segs[seg]._ds_va +
+                            map->dm_segs[seg].ds_len) == vaddr)) {
                                map->dm_segs[seg].ds_len += sgsize;
-                       else {
+                       } else {
                                if (++seg >= map->_dm_segcnt)
                                        break;
                                map->dm_segs[seg].ds_addr = curaddr;