From 3f03396918962b2f8b888d02b23cd1e0c88bf5e5 Mon Sep 17 00:00:00 2001 From: Marek Szyprowski Date: Tue, 24 May 2016 09:16:06 +0200 Subject: [PATCH] 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 Signed-off-by: Sylwester Nawrocki --- .../media/v4l2-core/videobuf2-dma-contig.c | 53 +++++++++++++++++++ include/media/videobuf2-dma-contig.h | 2 + 2 files changed, 55 insertions(+) diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c index 5361197f3e57..e3e47ace7daf 100644 --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c @@ -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 "); MODULE_LICENSE("GPL"); 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; -- 2.20.1