media: vb2-dma-contig: add helper for setting dma max seg size

Add a helper function for device drivers to set DMA's max_seg_size.
Setting it to largest possible value lets DMA-mapping API always create
contiguous mappings in DMA address space. This is essential for all
devices, which use dma-contig videobuf2 memory allocator and shared
buffers.

Till now, the only case when vb2-dma-contig really 'worked' was a case
where userspace provided USERPTR buffer, which was in fact mmaped
contiguous buffer from the other v4l2/drm device. Also DMABUF made of
contiguous buffer worked only when its exporter did not split it into
several chunks in the scatter-list. Any other buffer failed, regardless
of the arch/platform used and the presence of the IOMMU of the device bus.

This patch provides interface to fix this issue.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/media/videobuf2-dma-contig.h b/include/media/videobuf2-dma-contig.h
index 2087c9a68be3..f7dc8401817e 100644
--- a/include/media/videobuf2-dma-contig.h
+++ b/include/media/videobuf2-dma-contig.h
@@ -35,6 +35,8 @@ static inline void *vb2_dma_contig_init_ctx(struct device *dev)
 }
 
 void vb2_dma_contig_cleanup_ctx(void *alloc_ctx);
+int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size);
+void vb2_dma_contig_clear_max_seg_size(struct device *dev);
 
 extern const struct vb2_mem_ops vb2_dma_contig_memops;