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No functional changes. Remove a couple outdated or inane comments and

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add new comment blocks describing why the cache maintenance sequences are
done in the order they are for each case.
This commit is contained in:
Ian Lepore 2014-11-16 21:39:56 +00:00
parent 0c4f0ef9ae
commit a178f1f70a
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=274605
1 changed files with 35 additions and 5 deletions
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40
sys/arm/arm/busdma_machdep-v6.c
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@ -1314,17 +1314,20 @@ _bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
/*
* If the buffer was from user space, it is possible that this is not
* the same vm map, especially on a POST operation. It's not clear that
* dma on userland buffers can work at all right now, certainly not if a
* partial cacheline flush has to be handled. To be safe, until we're
* able to test direct userland dma, panic on a map mismatch.
* dma on userland buffers can work at all right now. To be safe, until
* we're able to test direct userland dma, panic on a map mismatch.
*/
if ((bpage = STAILQ_FIRST(&map->bpages)) != NULL) {
if (!pmap_dmap_iscurrent(map->pmap))
panic("_bus_dmamap_sync: wrong user map for bounce sync.");
/* Handle data bouncing. */
CTR4(KTR_BUSDMA, "%s: tag %p tag flags 0x%x op 0x%x "
"performing bounce", __func__, dmat, dmat->flags, op);
/*
* For PREWRITE do a writeback. Clean the caches from the
* innermost to the outermost levels.
*/
if (op & BUS_DMASYNC_PREWRITE) {
while (bpage != NULL) {
if (bpage->datavaddr != 0)
@ -1345,6 +1348,17 @@ _bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
dmat->bounce_zone->total_bounced++;
}
/*
* Do an invalidate for PREREAD unless a writeback was already
* done above due to PREWRITE also being set. The reason for a
* PREREAD invalidate is to prevent dirty lines currently in the
* cache from being evicted during the DMA. If a writeback was
* done due to PREWRITE also being set there will be no dirty
* lines and the POSTREAD invalidate handles the rest. The
* invalidate is done from the innermost to outermost level. If
* L2 were done first, a dirty cacheline could be automatically
* evicted from L1 before we invalidated it, re-dirtying the L2.
*/
if ((op & BUS_DMASYNC_PREREAD) && !(op & BUS_DMASYNC_PREWRITE)) {
bpage = STAILQ_FIRST(&map->bpages);
while (bpage != NULL) {
@ -1356,6 +1370,16 @@ _bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
bpage = STAILQ_NEXT(bpage, links);
}
}
/*
* Re-invalidate the caches on a POSTREAD, even though they were
* already invalidated at PREREAD time. Aggressive prefetching
* due to accesses to other data near the dma buffer could have
* brought buffer data into the caches which is now stale. The
* caches are invalidated from the outermost to innermost; the
* prefetches could be happening right now, and if L1 were
* invalidated first, stale L2 data could be prefetched into L1.
*/
if (op & BUS_DMASYNC_POSTREAD) {
while (bpage != NULL) {
vm_offset_t startv;
@ -1404,10 +1428,16 @@ _bus_dmamap_sync(bus_dma_tag_t dmat, bus_dmamap_t map, bus_dmasync_op_t op)
return;
}
/*
* Cache maintenance for normal (non-COHERENT non-bounce) buffers. All
* the comments about the sequences for flushing cache levels in the
* bounce buffer code above apply here as well. In particular, the fact
* that the sequence is inner-to-outer for PREREAD invalidation and
* outer-to-inner for POSTREAD invalidation is not a mistake.
*/
if (map->sync_count != 0) {
if (!pmap_dmap_iscurrent(map->pmap))
panic("_bus_dmamap_sync: wrong user map for sync.");
/* ARM caches are not self-snooping for dma */
sl = &map->slist[0];
end = &map->slist[map->sync_count];