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Allocate right number of pages for the bounced buffers crossing the page.

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One of the disadvantages of our current busdma code is the fact that
we process the bounced buffer in a page-by-page manner. This means that
the short (subpage) buffer allocated across page boundaries is bounced
to 2 separate pages.

This suboptimal behavior is consistent across all platforms and can be
related to (probably unimplementable or incompatible with bouncing)
BUS_DMA_KEEP_PG_OFFSET flag.

Therefore, allocate one additional page to be fully comply with this
requirement.

Discused with:	markj
PR:		251018
This commit is contained in:
Michal Meloun 2020-12-16 14:36:57 +00:00
parent 546114d08e
commit c0ffd35cbb
1 changed files with 13 additions and 5 deletions
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18
sys/arm64/arm64/busdma_bounce.c
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@ -297,6 +297,12 @@ bounce_bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
if ((flags & BUS_DMA_ALLOCNOW) != 0) {
struct bounce_zone *bz;
/*
* Round size up to a full page, and add one more page because
* there can always be one more boundary crossing than the
* number of pages in a transfer.
*/
maxsize = roundup2(maxsize, PAGE_SIZE) + PAGE_SIZE;
/* Must bounce */
if ((error = alloc_bounce_zone(newtag)) != 0) {
@ -308,7 +314,7 @@ bounce_bus_dma_tag_create(bus_dma_tag_t parent, bus_size_t alignment,
if (ptoa(bz->total_bpages) < maxsize) {
int pages;
pages = atop(round_page(maxsize)) - bz->total_bpages;
pages = atop(maxsize) + 1 - bz->total_bpages;
/* Add pages to our bounce pool */
if (alloc_bounce_pages(newtag, pages) < pages)
@ -436,8 +442,10 @@ bounce_bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
bz = dmat->bounce_zone;
/*
* Attempt to add pages to our pool on a per-instance
* basis up to a sane limit.
* Attempt to add pages to our pool on a per-instancebasis up to a sane
* limit. Even if the tag isn't subject of bouncing due to alignment
* and boundary constraints, it could still auto-bounce due to
* cacheline alignment, which requires at most two bounce pages.
*/
if (dmat->common.alignment > 1)
maxpages = MAX_BPAGES;
@ -446,9 +454,9 @@ bounce_bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
atop(dmat->common.lowaddr));
if ((dmat->bounce_flags & BF_MIN_ALLOC_COMP) == 0 ||
(bz->map_count > 0 && bz->total_bpages < maxpages)) {
pages = MAX(atop(dmat->common.maxsize), 1);
pages = atop(roundup2(dmat->common.maxsize, PAGE_SIZE)) + 1;
pages = MIN(maxpages - bz->total_bpages, pages);
pages = MAX(pages, 1);
pages = MAX(pages, 2);
if (alloc_bounce_pages(dmat, pages) < pages)
error = ENOMEM;
if ((dmat->bounce_flags & BF_MIN_ALLOC_COMP) == 0) {