Use define to test bounce buffer in amd64 bus dma.

To debug bounce buffers easily on non-SEV hardware, introduce a
define FORCE_BOUNCE_BUFFER that activates them.  Default is off,
no functional change.

OK miod@

diff --git a/sys/arch/amd64/amd64/bus_dma.c b/sys/arch/amd64/amd64/bus_dma.c
index 1d58dfc..6ad6583 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 1.52 2024/08/14 18:31:33 bluhm Exp $      */
+/*     $OpenBSD: bus_dma.c,v 1.53 2024/08/18 21:04:29 bluhm Exp $      */
 /*     $NetBSD: bus_dma.c,v 1.3 2003/05/07 21:33:58 fvdl Exp $ */
 
 /*-
@@ -96,6 +96,11 @@
 
 #include <uvm/uvm_extern.h>
 
+/* #define FORCE_BOUNCE_BUFFER 1 */
+#ifndef FORCE_BOUNCE_BUFFER
+#define FORCE_BOUNCE_BUFFER    0
+#endif
+
 int _bus_dmamap_load_buffer(bus_dma_tag_t, bus_dmamap_t, void *, bus_size_t,
     struct proc *, int, paddr_t *, int *, int);
 
@@ -115,6 +120,8 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_size_t size, int nsegments,
        void *mapstore;
        int npages, error;
        const struct kmem_dyn_mode *kd;
+       /* allocate and use bounce buffers when running as SEV guest */
+       int use_bounce_buffer = cpu_sev_guestmode || FORCE_BOUNCE_BUFFER;
 
        /*
         * Allocate and initialize the DMA map.  The end of the map
@@ -131,8 +138,7 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_size_t size, int nsegments,
        mapsize = sizeof(struct bus_dmamap) +
            (sizeof(bus_dma_segment_t) * (nsegments - 1));
 
-       /* allocate and use bounce buffers when running as SEV guest */
-       if (cpu_sev_guestmode) {
+       if (use_bounce_buffer) {
                /* this many pages plus one in case we get split */
                npages = round_page(size) / PAGE_SIZE + 1;
                if (npages < nsegments)
@@ -150,13 +156,13 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_size_t size, int nsegments,
        map->_dm_segcnt = nsegments;
        map->_dm_maxsegsz = maxsegsz;
        map->_dm_boundary = boundary;
-       if (cpu_sev_guestmode) {
+       if (use_bounce_buffer) {
                map->_dm_pages = (void *)&map->dm_segs[nsegments];
                map->_dm_npages = npages;
        }
        map->_dm_flags = flags & ~(BUS_DMA_WAITOK|BUS_DMA_NOWAIT);
 
-       if (!cpu_sev_guestmode) {
+       if (!use_bounce_buffer) {
                *dmamp = map;
                return (0);
        }
@@ -478,8 +484,9 @@ _bus_dmamap_sync(bus_dma_tag_t t, bus_dmamap_t map, bus_addr_t addr,
        bus_dma_segment_t *sg;
        int i, off = addr;
        bus_size_t l;
+       int use_bounce_buffer = cpu_sev_guestmode || FORCE_BOUNCE_BUFFER;
 
-       if (!cpu_sev_guestmode)
+       if (!use_bounce_buffer)
                return;
 
        for (i = map->_dm_segcnt, sg = map->dm_segs; size && i--; sg++) {
@@ -685,6 +692,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map, void *buf,
        int seg, page, off;
        pmap_t pmap;
        struct vm_page *pg;
+       int use_bounce_buffer = cpu_sev_guestmode || FORCE_BOUNCE_BUFFER;
 
        if (p != NULL)
                pmap = p->p_vmspace->vm_map.pmap;
@@ -705,8 +713,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map, void *buf,
                        panic("Non dma-reachable buffer at curaddr %#lx(raw)",
                            curaddr);
 
-               if (cpu_sev_guestmode) {
-                       /* use bounce buffer */
+               if (use_bounce_buffer) {
                        if (map->_dm_nused + 1 >= map->_dm_npages)
                                return (ENOMEM);