The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/busdma_machdep.c

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    1 /*
    2  * Copyright (c) 1997, 1998 Justin T. Gibbs.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions, and the following disclaimer,
   10  *    without modification, immediately at the beginning of the file.
   11  * 2. The name of the author may not be used to endorse or promote products
   12  *    derived from this software without specific prior written permission.
   13  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE FOR
   18  * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD$
   27  */
   28 
   29 #include <sys/param.h>
   30 #include <sys/systm.h>
   31 #include <sys/malloc.h>
   32 
   33 #include <vm/vm.h>
   34 #include <vm/vm_prot.h>
   35 #include <vm/vm_page.h>
   36 
   37 #include <machine/bus.h>
   38 #include <machine/md_var.h>
   39 
   40 #define MAX(a,b) (((a) > (b)) ? (a) : (b))
   41 #define MIN(a,b) (((a) < (b)) ? (a) : (b))
   42 #define MAX_BPAGES 128
   43 
   44 struct bus_dma_tag {
   45         bus_dma_tag_t     parent;
   46         bus_size_t        alignment;
   47         bus_size_t        boundary;
   48         bus_addr_t        lowaddr;
   49         bus_addr_t        highaddr;
   50         bus_dma_filter_t *filter;
   51         void             *filterarg;
   52         bus_size_t        maxsize;
   53         u_int             nsegments;
   54         bus_size_t        maxsegsz;
   55         int               flags;
   56         int               ref_count;
   57         int               map_count;
   58 };
   59 
   60 struct bounce_page {
   61         vm_offset_t     vaddr;          /* kva of bounce buffer */
   62         bus_addr_t      busaddr;        /* Physical address */
   63         vm_offset_t     datavaddr;      /* kva of client data */
   64         bus_size_t      datacount;      /* client data count */
   65         STAILQ_ENTRY(bounce_page) links;
   66 };
   67 
   68 int busdma_swi_pending;
   69 
   70 static STAILQ_HEAD(bp_list, bounce_page) bounce_page_list;
   71 static int free_bpages;
   72 static int reserved_bpages;
   73 static int active_bpages;
   74 static int total_bpages;
   75 static bus_addr_t bounce_lowaddr = BUS_SPACE_MAXADDR;
   76 
   77 struct bus_dmamap {
   78         struct bp_list         bpages;
   79         int                    pagesneeded;
   80         int                    pagesreserved;
   81         bus_dma_tag_t          dmat;
   82         void                  *buf;             /* unmapped buffer pointer */
   83         bus_size_t             buflen;          /* unmapped buffer length */
   84         bus_dmamap_callback_t *callback;
   85         void                  *callback_arg;
   86         STAILQ_ENTRY(bus_dmamap) links;
   87 };
   88 
   89 static STAILQ_HEAD(, bus_dmamap) bounce_map_waitinglist;
   90 static STAILQ_HEAD(, bus_dmamap) bounce_map_callbacklist;
   91 static struct bus_dmamap nobounce_dmamap;
   92 
   93 static int alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages);
   94 static int reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map);
   95 static vm_offset_t add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map,
   96                                    vm_offset_t vaddr, bus_size_t size);
   97 static void free_bounce_page(bus_dma_tag_t dmat, struct bounce_page *bpage);
   98 static __inline int run_filter(bus_dma_tag_t dmat, bus_addr_t paddr);
   99 
  100 static __inline int
  101 run_filter(bus_dma_tag_t dmat, bus_addr_t paddr)
  102 {
  103         int retval;
  104 
  105         retval = 0;
  106         do {
  107                 if (paddr > dmat->lowaddr
  108                  && paddr <= dmat->highaddr
  109                  && (dmat->filter == NULL
  110                   || (*dmat->filter)(dmat->filterarg, paddr) != 0))
  111                         retval = 1;
  112 
  113                 dmat = dmat->parent;            
  114         } while (retval == 0 && dmat != NULL);
  115         return (retval);
  116 }
  117 
  118 #define BUS_DMA_MIN_ALLOC_COMP BUS_DMA_BUS4
  119 /*
  120  * Allocate a device specific dma_tag.
  121  */
  122 int
  123 bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
  124                    bus_size_t boundary, bus_addr_t lowaddr,
  125                    bus_addr_t highaddr, bus_dma_filter_t *filter,
  126                    void *filterarg, bus_size_t maxsize, int nsegments,
  127                    bus_size_t maxsegsz, int flags, bus_dma_tag_t *dmat)
  128 {
  129         bus_dma_tag_t newtag;
  130         int error = 0;
  131 
  132         /* Return a NULL tag on failure */
  133         *dmat = NULL;
  134 
  135         newtag = (bus_dma_tag_t)malloc(sizeof(*newtag), M_DEVBUF, M_NOWAIT);
  136         if (newtag == NULL)
  137                 return (ENOMEM);
  138 
  139         newtag->parent = parent;
  140         newtag->boundary = boundary;
  141         newtag->lowaddr = trunc_page((vm_offset_t)lowaddr) + (PAGE_SIZE - 1);
  142         newtag->highaddr = trunc_page((vm_offset_t)highaddr) + (PAGE_SIZE - 1);
  143         newtag->filter = filter;
  144         newtag->filterarg = filterarg;
  145         newtag->maxsize = maxsize;
  146         newtag->nsegments = nsegments;
  147         newtag->maxsegsz = maxsegsz;
  148         newtag->flags = flags;
  149         newtag->ref_count = 1; /* Count ourself */
  150         newtag->map_count = 0;
  151         
  152         /* Take into account any restrictions imposed by our parent tag */
  153         if (parent != NULL) {
  154                 newtag->lowaddr = MIN(parent->lowaddr, newtag->lowaddr);
  155                 newtag->highaddr = MAX(parent->highaddr, newtag->highaddr);
  156                 /*
  157                  * XXX Not really correct??? Probably need to honor boundary
  158                  *     all the way up the inheritence chain.
  159                  */
  160                 newtag->boundary = MAX(parent->boundary, newtag->boundary);
  161                 if (newtag->filter == NULL) {
  162                         /*
  163                          * Short circuit looking at our parent directly
  164                          * since we have encapsulated all of its information
  165                          */
  166                         newtag->filter = parent->filter;
  167                         newtag->filterarg = parent->filterarg;
  168                         newtag->parent = parent->parent;
  169                 }
  170                 if (newtag->parent != NULL) {
  171                         parent->ref_count++;
  172                 }
  173         }
  174         
  175         if (newtag->lowaddr < ptoa(Maxmem) && (flags & BUS_DMA_ALLOCNOW) != 0) {
  176                 /* Must bounce */
  177 
  178                 if (lowaddr > bounce_lowaddr) {
  179                         /*
  180                          * Go through the pool and kill any pages
  181                          * that don't reside below lowaddr.
  182                          */
  183                         panic("bus_dma_tag_create: page reallocation "
  184                               "not implemented");
  185                 }
  186                 if (ptoa(total_bpages) < maxsize) {
  187                         int pages;
  188 
  189                         pages = atop(maxsize) - total_bpages;
  190 
  191                         /* Add pages to our bounce pool */
  192                         if (alloc_bounce_pages(newtag, pages) < pages)
  193                                 error = ENOMEM;
  194                 }
  195                 /* Performed initial allocation */
  196                 newtag->flags |= BUS_DMA_MIN_ALLOC_COMP;
  197         }
  198         
  199         if (error != 0) {
  200                 free(newtag, M_DEVBUF);
  201         } else {
  202                 *dmat = newtag;
  203         }
  204         return (error);
  205 }
  206 
  207 int
  208 bus_dma_tag_destroy(bus_dma_tag_t dmat)
  209 {
  210         if (dmat != NULL) {
  211 
  212                 if (dmat->map_count != 0)
  213                         return (EBUSY);
  214 
  215                 while (dmat != NULL) {
  216                         bus_dma_tag_t parent;
  217 
  218                         parent = dmat->parent;
  219                         dmat->ref_count--;
  220                         if (dmat->ref_count == 0) {
  221                                 free(dmat, M_DEVBUF);
  222                                 /*
  223                                  * Last reference count, so
  224                                  * release our reference
  225                                  * count on our parent.
  226                                  */
  227                                 dmat = parent;
  228                         } else
  229                                 dmat = NULL;
  230                 }
  231         }
  232         return (0);
  233 }
  234 
  235 /*
  236  * Allocate a handle for mapping from kva/uva/physical
  237  * address space into bus device space.
  238  */
  239 int
  240 bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
  241 {
  242         int error;
  243 
  244         error = 0;
  245 
  246         if (dmat->lowaddr < ptoa(Maxmem)) {
  247                 /* Must bounce */
  248                 int maxpages;
  249 
  250                 *mapp = (bus_dmamap_t)malloc(sizeof(**mapp), M_DEVBUF,
  251                                              M_NOWAIT);
  252                 if (*mapp == NULL) {
  253                         return (ENOMEM);
  254                 } else {
  255                         /* Initialize the new map */
  256                         bzero(*mapp, sizeof(**mapp));
  257                         STAILQ_INIT(&((*mapp)->bpages));
  258                 }
  259                 /*
  260                  * Attempt to add pages to our pool on a per-instance
  261                  * basis up to a sane limit.
  262                  */
  263                 maxpages = MIN(MAX_BPAGES, Maxmem - atop(dmat->lowaddr));
  264                 if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0
  265                  || (dmat->map_count > 0
  266                   && total_bpages < maxpages)) {
  267                         int pages;
  268 
  269                         if (dmat->lowaddr > bounce_lowaddr) {
  270                                 /*
  271                                  * Go through the pool and kill any pages
  272                                  * that don't reside below lowaddr.
  273                                  */
  274                                 panic("bus_dmamap_create: page reallocation "
  275                                       "not implemented");
  276                         }
  277                         pages = atop(dmat->maxsize);
  278                         pages = MIN(maxpages - total_bpages, pages);
  279                         error = alloc_bounce_pages(dmat, pages);
  280 
  281                         if ((dmat->flags & BUS_DMA_MIN_ALLOC_COMP) == 0) {
  282                                 if (error == 0)
  283                                         dmat->flags |= BUS_DMA_MIN_ALLOC_COMP;
  284                         } else {
  285                                 error = 0;
  286                         }
  287                 }
  288         } else {
  289                 *mapp = NULL;
  290         }
  291         if (error == 0)
  292                 dmat->map_count++;
  293         return (error);
  294 }
  295 
  296 /*
  297  * Destroy a handle for mapping from kva/uva/physical
  298  * address space into bus device space.
  299  */
  300 int
  301 bus_dmamap_destroy(bus_dma_tag_t dmat, bus_dmamap_t map)
  302 {
  303         if (map != NULL) {
  304                 if (STAILQ_FIRST(&map->bpages) != NULL)
  305                         return (EBUSY);
  306                 free(map, M_DEVBUF);
  307         }
  308         dmat->map_count--;
  309         return (0);
  310 }
  311 
  312 
  313 /*
  314  * Allocate a piece of memory that can be efficiently mapped into
  315  * bus device space based on the constraints lited in the dma tag.
  316  * A dmamap to for use with dmamap_load is also allocated.
  317  */
  318 int
  319 bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
  320                  bus_dmamap_t *mapp)
  321 {
  322         /* If we succeed, no mapping/bouncing will be required */
  323         *mapp = NULL;
  324 
  325         if ((dmat->maxsize <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem)) {
  326                 *vaddr = malloc(dmat->maxsize, M_DEVBUF,
  327                                 (flags & BUS_DMA_NOWAIT) ? M_NOWAIT : M_WAITOK);
  328         } else {
  329                 /*
  330                  * XXX Use Contigmalloc until it is merged into this facility
  331                  *     and handles multi-seg allocations.  Nobody is doing
  332                  *     multi-seg allocations yet though.
  333                  */
  334                 *vaddr = contigmalloc(dmat->maxsize, M_DEVBUF,
  335                                       (flags & BUS_DMA_NOWAIT)
  336                                       ? M_NOWAIT : M_WAITOK,
  337                                       0ul, dmat->lowaddr, 1ul, dmat->boundary);
  338         }
  339         if (*vaddr == NULL)
  340                 return (ENOMEM);
  341         return (0);
  342 }
  343 
  344 /*
  345  * Free a piece of memory and it's allociated dmamap, that was allocated
  346  * via bus_dmamem_alloc.
  347  */
  348 void
  349 bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
  350 {
  351         /*
  352          * dmamem does not need to be bounced, so the map should be
  353          * NULL
  354          */
  355         if (map != NULL)
  356                 panic("bus_dmamem_free: Invalid map freed\n");
  357         /* XXX There is no "contigfree" and "free" doesn't work */
  358         if ((dmat->maxsize <= PAGE_SIZE) && dmat->lowaddr >= ptoa(Maxmem))
  359                 free(vaddr, M_DEVBUF);
  360 }
  361 
  362 #define BUS_DMAMAP_NSEGS ((BUS_SPACE_MAXSIZE / PAGE_SIZE) + 1)
  363 
  364 /*
  365  * Map the buffer buf into bus space using the dmamap map.
  366  */
  367 int
  368 bus_dmamap_load(bus_dma_tag_t dmat, bus_dmamap_t map, void *buf,
  369                 bus_size_t buflen, bus_dmamap_callback_t *callback,
  370                 void *callback_arg, int flags)
  371 {
  372         vm_offset_t             vaddr;
  373         vm_offset_t             paddr;
  374 #ifdef __GNUC__
  375         bus_dma_segment_t       dm_segments[dmat->nsegments];
  376 #else
  377         bus_dma_segment_t       dm_segments[BUS_DMAMAP_NSEGS];
  378 #endif
  379         bus_dma_segment_t      *sg;
  380         int                     seg;
  381         int                     error;
  382 
  383         if (map == NULL)
  384                 map = &nobounce_dmamap;
  385 
  386         error = 0;
  387         /*
  388          * If we are being called during a callback, pagesneeded will
  389          * be non-zero, so we can avoid doing the work twice.
  390          */
  391         if (dmat->lowaddr < ptoa(Maxmem) && map->pagesneeded == 0) {
  392                 vm_offset_t     vendaddr;
  393 
  394                 /*
  395                  * Count the number of bounce pages
  396                  * needed in order to complete this transfer
  397                  */
  398                 vaddr = trunc_page((vm_offset_t)buf);
  399                 vendaddr = (vm_offset_t)buf + buflen;
  400 
  401                 while (vaddr < vendaddr) {
  402                         paddr = pmap_kextract(vaddr);
  403                         if (run_filter(dmat, paddr) != 0) {
  404 
  405                                 map->pagesneeded++;
  406                         }
  407                         vaddr += PAGE_SIZE;
  408                 }
  409         }
  410 
  411         /* Reserve Necessary Bounce Pages */
  412         if (map->pagesneeded != 0) {
  413                 int s;
  414 
  415                 s = splhigh();
  416                 if (reserve_bounce_pages(dmat, map) != 0) {
  417 
  418                         /* Queue us for resources */
  419                         map->dmat = dmat;
  420                         map->buf = buf;
  421                         map->buflen = buflen;
  422                         map->callback = callback;
  423                         map->callback_arg = callback_arg;
  424 
  425                         STAILQ_INSERT_TAIL(&bounce_map_waitinglist, map, links);
  426                         splx(s);
  427 
  428                         return (EINPROGRESS);
  429                 }
  430                 splx(s);
  431         }
  432 
  433         vaddr = (vm_offset_t)buf;
  434         sg = &dm_segments[0];
  435         seg = 1;
  436         sg->ds_len = 0;
  437 
  438         {
  439                 /*
  440                  * note: nextpaddr not used on first loop
  441                  */
  442                 vm_offset_t     nextpaddr = 0;
  443 
  444                 do {
  445                         bus_size_t      size;
  446 
  447                         paddr = pmap_kextract(vaddr);
  448                         size = PAGE_SIZE - (paddr & PAGE_MASK);
  449                         if (size > buflen)
  450                                 size = buflen;
  451 
  452                         if (map->pagesneeded != 0
  453                          && run_filter(dmat, paddr)) {
  454                                 paddr = add_bounce_page(dmat, map, 
  455                                     vaddr, size);
  456                         }
  457 
  458                         if (sg->ds_len == 0) {
  459                                 sg->ds_addr = paddr;
  460                                 sg->ds_len = size;
  461                         } else if (paddr == nextpaddr) {
  462                                 sg->ds_len += size;
  463                         } else {
  464                                 /* Go to the next segment */
  465                                 sg++;
  466                                 seg++;
  467                                 if (seg > dmat->nsegments)
  468                                         break;
  469                                 sg->ds_addr = paddr;
  470                                 sg->ds_len = size;
  471                         }
  472                         vaddr += size;
  473                         nextpaddr = paddr + size;
  474                         buflen -= size;
  475                 } while (buflen > 0);
  476         }
  477 
  478         if (buflen != 0) {
  479                 printf("bus_dmamap_load: Too many segs! buf_len = 0x%lx\n",
  480                        (u_long)buflen);
  481                 error = EFBIG;
  482         }
  483 
  484         (*callback)(callback_arg, dm_segments, seg, error);
  485 
  486         return (0);
  487 }
  488 
  489 /*
  490  * Release the mapping held by map.
  491  */
  492 void
  493 _bus_dmamap_unload(bus_dma_tag_t dmat, bus_dmamap_t map)
  494 {
  495         struct bounce_page *bpage;
  496 
  497         while ((bpage = STAILQ_FIRST(&map->bpages)) != NULL) {
  498                 STAILQ_REMOVE_HEAD(&map->bpages, links);
  499                 free_bounce_page(dmat, bpage);
  500         }
  501 }
  502 
  503 void
  504 _bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
  505 {
  506         struct bounce_page *bpage;
  507 
  508         if ((bpage = STAILQ_FIRST(&map->bpages)) != NULL) {
  509                 
  510                 /*
  511                  * Handle data bouncing.  We might also
  512                  * want to add support for invalidating
  513                  * the caches on broken hardware
  514                  */
  515                 switch (op) {
  516                 case BUS_DMASYNC_PREWRITE:
  517                         while (bpage != NULL) {
  518                                 bcopy((void *)bpage->datavaddr,
  519                                       (void *)bpage->vaddr,
  520                                       bpage->datacount);
  521                                 bpage = STAILQ_NEXT(bpage, links);
  522                         }
  523                         break;
  524 
  525                 case BUS_DMASYNC_POSTREAD:
  526                         while (bpage != NULL) {
  527                                 bcopy((void *)bpage->vaddr,
  528                                       (void *)bpage->datavaddr,
  529                                       bpage->datacount);
  530                                 bpage = STAILQ_NEXT(bpage, links);
  531                         }
  532                         break;
  533                 case BUS_DMASYNC_PREREAD:
  534                 case BUS_DMASYNC_POSTWRITE:
  535                         /* No-ops */
  536                         break;
  537                 }
  538         }
  539 }
  540 
  541 static int
  542 alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
  543 {
  544         int count;
  545 
  546         count = 0;
  547         if (total_bpages == 0) {
  548                 STAILQ_INIT(&bounce_page_list);
  549                 STAILQ_INIT(&bounce_map_waitinglist);
  550                 STAILQ_INIT(&bounce_map_callbacklist);
  551         }
  552         
  553         while (numpages > 0) {
  554                 struct bounce_page *bpage;
  555                 int s;
  556 
  557                 bpage = (struct bounce_page *)malloc(sizeof(*bpage), M_DEVBUF,
  558                                                      M_NOWAIT);
  559 
  560                 if (bpage == NULL)
  561                         break;
  562                 bzero(bpage, sizeof(*bpage));
  563                 bpage->vaddr = (vm_offset_t)contigmalloc(PAGE_SIZE, M_DEVBUF,
  564                                                          M_NOWAIT, 0ul,
  565                                                          dmat->lowaddr,
  566                                                          PAGE_SIZE,
  567                                                          0);
  568                 if (bpage->vaddr == NULL) {
  569                         free(bpage, M_DEVBUF);
  570                         break;
  571                 }
  572                 bpage->busaddr = pmap_kextract(bpage->vaddr);
  573                 s = splhigh();
  574                 STAILQ_INSERT_TAIL(&bounce_page_list, bpage, links);
  575                 total_bpages++;
  576                 free_bpages++;
  577                 splx(s);
  578                 count++;
  579                 numpages--;
  580         }
  581         return (count);
  582 }
  583 
  584 static int
  585 reserve_bounce_pages(bus_dma_tag_t dmat, bus_dmamap_t map)
  586 {
  587         int pages;
  588 
  589         pages = MIN(free_bpages, map->pagesneeded - map->pagesreserved);
  590         free_bpages -= pages;
  591         reserved_bpages += pages;
  592         map->pagesreserved += pages;
  593         pages = map->pagesneeded - map->pagesreserved;
  594 
  595         return (pages);
  596 }
  597 
  598 static vm_offset_t
  599 add_bounce_page(bus_dma_tag_t dmat, bus_dmamap_t map, vm_offset_t vaddr,
  600                 bus_size_t size)
  601 {
  602         int s;
  603         struct bounce_page *bpage;
  604 
  605         if (map->pagesneeded == 0)
  606                 panic("add_bounce_page: map doesn't need any pages");
  607         map->pagesneeded--;
  608 
  609         if (map->pagesreserved == 0)
  610                 panic("add_bounce_page: map doesn't need any pages");
  611         map->pagesreserved--;
  612 
  613         s = splhigh();
  614         bpage = STAILQ_FIRST(&bounce_page_list);
  615         if (bpage == NULL)
  616                 panic("add_bounce_page: free page list is empty");
  617 
  618         STAILQ_REMOVE_HEAD(&bounce_page_list, links);
  619         reserved_bpages--;
  620         active_bpages++;
  621         splx(s);
  622 
  623         bpage->datavaddr = vaddr;
  624         bpage->datacount = size;
  625         STAILQ_INSERT_TAIL(&(map->bpages), bpage, links);
  626         return (bpage->busaddr);
  627 }
  628 
  629 static void
  630 free_bounce_page(bus_dma_tag_t dmat, struct bounce_page *bpage)
  631 {
  632         int s;
  633         struct bus_dmamap *map;
  634 
  635         bpage->datavaddr = 0;
  636         bpage->datacount = 0;
  637 
  638         s = splhigh();
  639         STAILQ_INSERT_HEAD(&bounce_page_list, bpage, links);
  640         free_bpages++;
  641         active_bpages--;
  642         if ((map = STAILQ_FIRST(&bounce_map_waitinglist)) != NULL) {
  643                 if (reserve_bounce_pages(map->dmat, map) == 0) {
  644                         STAILQ_REMOVE_HEAD(&bounce_map_waitinglist, links);
  645                         STAILQ_INSERT_TAIL(&bounce_map_callbacklist,
  646                                            map, links);
  647                         busdma_swi_pending = 1;
  648                         setsoftvm();
  649                 }
  650         }
  651         splx(s);
  652 }
  653 
  654 void
  655 busdma_swi()
  656 {
  657         int s;
  658         struct bus_dmamap *map;
  659 
  660         s = splhigh();
  661         while ((map = STAILQ_FIRST(&bounce_map_callbacklist)) != NULL) {
  662                 STAILQ_REMOVE_HEAD(&bounce_map_callbacklist, links);
  663                 splx(s);
  664                 bus_dmamap_load(map->dmat, map, map->buf, map->buflen,
  665                                 map->callback, map->callback_arg, /*flags*/0);
  666                 s = splhigh();
  667         }
  668         splx(s);
  669 }

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