The system heap currently allocates each backing page no larger than the remaining dma-buf length. It can therefore use the complete compound-page size for every scatterlist entry while keeping the total length equal to the buffer size.
Shared backing allocations may need to be rounded up to an architecture shared granule size. A backing allocation can then be larger than the remaining buffer length. Describing the complete allocation in the scatterlist would incorrectly expose the rounded tail to scatterlist consumers as part of the dma-buf.
Track the remaining buffer length while constructing the scatterlist and limit each entry to the smaller of the compound-page size and the remaining length. The complete backing allocation remains owned by the heap and is still released normally.
This does not change behavior with the current allocation policy, but prepares the heap for shared-granule-sized backing allocations.
Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Benjamin Gaignard benjamin.gaignard@collabora.com Cc: Brian Starkey Brian.Starkey@arm.com Cc: John Stultz jstultz@google.com Cc: "T.J. Mercier" tjmercier@google.com Cc: "Christian König" christian.koenig@amd.com Signed-off-by: Aneesh Kumar K.V (Arm) aneesh.kumar@kernel.org --- drivers/dma-buf/heaps/system_heap.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c index c8959eadc71d..b5b8cdf65f23 100644 --- a/drivers/dma-buf/heaps/system_heap.c +++ b/drivers/dma-buf/heaps/system_heap.c @@ -406,6 +406,7 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap, struct system_heap_buffer *buffer; DEFINE_DMA_BUF_EXPORT_INFO(exp_info); unsigned long size_remaining = len; + unsigned long sg_remaining = len; unsigned int max_order = orders[0]; struct system_heap_priv *priv = dma_heap_get_drvdata(heap); bool cc_shared = priv->cc_shared; @@ -454,7 +455,11 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
sg = table->sgl; list_for_each_entry_safe(page, tmp_page, &pages, lru) { - sg_set_page(sg, page, page_size(page), 0); + unsigned long sg_len; + + sg_len = min_t(unsigned long, page_size(page), sg_remaining); + sg_set_page(sg, page, sg_len, 0); + sg_remaining -= sg_len; sg = sg_next(sg); list_del(&page->lru); }