cma_heap_attach() merges the physically contiguous buffer into one
scatterlist entry without considering the importing device's maximum
segment size. With DMA_API_DEBUG, importing a buffer larger than that
limit reports, here with atmel-hlcdc:
DMA-API: atmel-hlcdc-display-controller atmel-hlcdc-dc: mapping sg
segment longer than device claims to support [len=307200] [max=65536]
Build each attachment table using the importing device's segment limit.
Return -EINVAL if the limit is smaller than PAGE_SIZE because the
page-based allocator cannot honor it.
An importer that needs the whole buffer as one entry has to declare a
segment size that covers it. tegra-vde without an IOMMU domain and
armada did not. Their limits must be raised before this change is
applied.
Reproduced with a custom QEMU model of the SAM9X75 Curiosity. Not
tested on real hardware.
Fixes: b61614ec318a ("dma-buf: heaps: Add CMA heap to dmabuf heaps")
Cc: [email protected] # needs the tegra-vde and armada segment size
changes first
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <[email protected]>
---
Notes:
Tested on v7.3-rc4-70-gfe2ec83746e5 with DMA_API_DEBUG and
DMABUF_DEBUG, on a custom QEMU model of the SAM9X75 Curiosity
(ARM926EJ-S, TCG) with an XLCDC model.
vivid captures into three 307200-byte CMA heap buffers, which
atmel-hlcdc imports and scans out. All 8 frames are shown before and
after the patch, with 3 DMA-API reports before and none after.
A test importer maps a 256 KiB CMA heap buffer with different
maximum segment sizes (4 KiB pages):
max segment (bytes) before after
2048 1 x 256 KiB attach returns -EINVAL
4096 1 x 256 KiB 64 x 4 KiB
65536 1 x 256 KiB 4 x 64 KiB
UINT_MAX 1 x 256 KiB 1 x 256 KiB
The first three cases gave a DMA-API report before the patch and
none after it.
drivers/dma-buf/heaps/cma_heap.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index 3fb4b946c91a..9d61d14688b8 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -58,16 +58,22 @@ static int cma_heap_attach(struct dma_buf *dmabuf,
{
struct cma_heap_buffer *buffer = dmabuf->priv;
struct dma_heap_attachment *a;
+ unsigned int max_segment;
int ret;
+ max_segment = dma_get_max_seg_size(attachment->dev);
+ /* The SG allocator requires a segment limit of at least PAGE_SIZE. */
+ if (max_segment < PAGE_SIZE)
+ return -EINVAL;
+
a = kzalloc_obj(*a);
if (!a)
return -ENOMEM;
- ret = sg_alloc_table_from_pages(&a->table, buffer->pages,
- buffer->pagecount, 0,
- buffer->pagecount << PAGE_SHIFT,
- GFP_KERNEL);
+ ret = sg_alloc_table_from_pages_segment(&a->table, buffer->pages,
+ buffer->pagecount, 0,
+ buffer->pagecount << PAGE_SHIFT,
+ max_segment, GFP_KERNEL);
if (ret) {
kfree(a);
return ret;
--
2.53.0
