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Commit 3f033969 authored by Marek Szyprowski's avatar Marek Szyprowski Committed by Sylwester Nawrocki
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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: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: default avatarSylwester Nawrocki <s.nawrocki@samsung.com>
parent c974c436

drivers/media/v4l2-core/videobuf2-dma-contig.c

+53 −0
Original line number Diff line number Diff line
@@ -753,6 +753,59 @@ void vb2_dma_contig_cleanup_ctx(void *alloc_ctx) 
}

EXPORT_SYMBOL_GPL(vb2_dma_contig_cleanup_ctx);



/**

 * vb2_dma_contig_set_max_seg_size() - configure DMA max segment size

 * @dev:	device for configuring DMA parameters

 * @size:	size of DMA max segment size to set

 *

 * To allow mapping the scatter-list into a single chunk in the DMA

 * address space, the device is required to have the DMA max segment

 * size parameter set to a value larger than the buffer size. Otherwise,

 * the DMA-mapping subsystem will split the mapping into max segment

 * size chunks. This function sets the DMA max segment size

 * parameter to let DMA-mapping map a buffer as a single chunk in DMA

 * address space.

 * This code assumes that the DMA-mapping subsystem will merge all

 * scatterlist segments if this is really possible (for example when

 * an IOMMU is available and enabled).

 * Ideally, this parameter should be set by the generic bus code, but it

 * is left with the default 64KiB value due to historical litmiations in

 * other subsystems (like limited USB host drivers) and there no good

 * place to set it to the proper value.

 * This function should be called from the drivers, which are known to

 * operate on platforms with IOMMU and provide access to shared buffers

 * (either USERPTR or DMABUF). This should be done before initializing

 * videobuf2 queue.

 */

int vb2_dma_contig_set_max_seg_size(struct device *dev, unsigned int size)

{

	if (!dev->dma_parms) {

		dev->dma_parms = kzalloc(sizeof(dev->dma_parms), GFP_KERNEL);

		if (!dev->dma_parms)

			return -ENOMEM;

	}

	if (dma_get_max_seg_size(dev) < size)

		return dma_set_max_seg_size(dev, size);



	return 0;

}

EXPORT_SYMBOL_GPL(vb2_dma_contig_set_max_seg_size);



/*

 * vb2_dma_contig_clear_max_seg_size() - release resources for DMA parameters

 * @dev:	device for configuring DMA parameters

 *

 * This function releases resources allocated to configure DMA parameters

 * (see vb2_dma_contig_set_max_seg_size() function). It should be called from

 * device drivers on driver remove.

 */

void vb2_dma_contig_clear_max_seg_size(struct device *dev)

{

	kfree(dev->dma_parms);

	dev->dma_parms = NULL;

}

EXPORT_SYMBOL_GPL(vb2_dma_contig_clear_max_seg_size);



MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2");

MODULE_AUTHOR("Pawel Osciak <pawel@osciak.com>");

MODULE_LICENSE("GPL");

include/media/videobuf2-dma-contig.h

+2 −0
Original line number Diff line number Diff line
@@ -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;