This patch lets vb2-dma-contig memory allocator to configure DMA max segment size properly for the client device. Setting it is needed to let DMA-mapping subsystem to create a single, contiguous mapping in DMA address space. This is essential for all devices, which use dma-contig videobuf2 memory allocator and shared buffers (in USERPTR or DMAbuf modes of operations). Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> --- Hello, This patch is a follow-up of my previous attempts to let Exynos multimedia devices to work properly with shared buffers when IOMMU is enabled: 1. https://www.mail-archive.com/linux-media@xxxxxxxxxxxxxxx/msg96946.html 2. http://thread.gmane.org/gmane.linux.drivers.video-input-infrastructure/97316 3. https://patchwork.linuxtv.org/patch/30870/ As sugested by Hans, configuring DMA max segment size should be done by videobuf2-dma-contig module instead of requiring all device drivers to do it on their own. Here is some backgroud why this is done in videobuf2-dc not in the respective generic bus code: http://lists.infradead.org/pipermail/linux-arm-kernel/2014-November/305913.html Best regards, Marek Szyprowski --- drivers/media/v4l2-core/videobuf2-dma-contig.c | 39 ++++++++++++++++++++++++++ 1 file changed, 39 insertions(+) diff --git a/drivers/media/v4l2-core/videobuf2-dma-contig.c b/drivers/media/v4l2-core/videobuf2-dma-contig.c index 461ae55eaa98..871e370f8e88 100644 --- a/drivers/media/v4l2-core/videobuf2-dma-contig.c +++ b/drivers/media/v4l2-core/videobuf2-dma-contig.c @@ -443,6 +443,35 @@ static void vb2_dc_put_userptr(void *buf_priv) } /* + * To allow mapping scatter-list into signle chunk in DMA address space, + * device is required to have DMA max segment size parameter set to value + * larger than the buffer size. Otherwise, DMA-mapping subsystem will + * split the mapping into max segment size chunks. + * This function increases DMA max segment size parameter to let + * DMA-mapping to map a buffer as a single chunk in DMA address space. + * This code assumes that the DMA-mapping subsystem will merge all + * scatter-list segments if this is really possible (for example when + * IOMMU is available and enabled). + * Ideally, this parameter should be set by generic bus code, but it is + * left with the default 64KiB value due to some historical limitations + * in other subsystems (like limited USB host drivers) and there is no + * good place to set it to the proper value. It is done here to avoid + * fixing all vb2-dc client drivers. + */ +static int vb2_dc_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; +} + +/* * For some kind of reserved memory there might be no struct page available, * so all that can be done to support such 'pages' is to try to convert * pfn to dma address or at the last resort just assume that @@ -499,6 +528,10 @@ static void *vb2_dc_get_userptr(struct device *dev, unsigned long vaddr, return ERR_PTR(-EINVAL); } + ret = vb2_dc_set_max_seg_size(dev, PAGE_ALIGN(size + PAGE_SIZE)); + if (!ret) + return ERR_PTR(ret); + buf = kzalloc(sizeof *buf, GFP_KERNEL); if (!buf) return ERR_PTR(-ENOMEM); @@ -675,10 +708,15 @@ static void *vb2_dc_attach_dmabuf(struct device *dev, struct dma_buf *dbuf, { struct vb2_dc_buf *buf; struct dma_buf_attachment *dba; + int ret; if (dbuf->size < size) return ERR_PTR(-EFAULT); + ret = vb2_dc_set_max_seg_size(dev, PAGE_ALIGN(size)); + if (!ret) + return ERR_PTR(ret); + buf = kzalloc(sizeof(*buf), GFP_KERNEL); if (!buf) return ERR_PTR(-ENOMEM); @@ -722,6 +760,7 @@ const struct vb2_mem_ops vb2_dma_contig_memops = { }; EXPORT_SYMBOL_GPL(vb2_dma_contig_memops); + MODULE_DESCRIPTION("DMA-contig memory handling routines for videobuf2"); MODULE_AUTHOR("Pawel Osciak <pawel@xxxxxxxxxx>"); MODULE_LICENSE("GPL"); -- 1.9.2 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
