Hi Anle, On Mon, Aug 28, 2023 at 8:57 AM Anle Pan <anle.pan@xxxxxxx> wrote: > > When allocating from pages, the size of the sg segment is unlimited and > the default is UINT_MAX. This will cause the DMA stream mapping failed > later with a "swiotlb buffer full" error. Thanks for the patch. Good catch. > The default maximum mapping > size is 128 slots x 2K = 256K, determined by "IO_TLB_SEGSIZE". > To fix the issue, limit the sg segment size according to > "dma_max_mapping_size" to match the mapping limit. > > Signed-off-by: Anle Pan <anle.pan@xxxxxxx> > --- > drivers/media/common/videobuf2/videobuf2-dma-sg.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/drivers/media/common/videobuf2/videobuf2-dma-sg.c b/drivers/media/common/videobuf2/videobuf2-dma-sg.c > index fa69158a65b1..b608a7c5f240 100644 > --- a/drivers/media/common/videobuf2/videobuf2-dma-sg.c > +++ b/drivers/media/common/videobuf2/videobuf2-dma-sg.c > @@ -105,6 +105,7 @@ static void *vb2_dma_sg_alloc(struct vb2_buffer *vb, struct device *dev, > struct sg_table *sgt; > int ret; > int num_pages; > + size_t max_segment = 0; > > if (WARN_ON(!dev) || WARN_ON(!size)) > return ERR_PTR(-EINVAL); > @@ -134,8 +135,12 @@ static void *vb2_dma_sg_alloc(struct vb2_buffer *vb, struct device *dev, > if (ret) > goto fail_pages_alloc; > > - ret = sg_alloc_table_from_pages(buf->dma_sgt, buf->pages, > - buf->num_pages, 0, size, GFP_KERNEL); > + if (dev) > + max_segment = dma_max_mapping_size(dev); > + if (max_segment == 0) > + max_segment = UINT_MAX; > + ret = sg_alloc_table_from_pages_segment(buf->dma_sgt, buf->pages, > + buf->num_pages, 0, size, max_segment, GFP_KERNEL); One thing that I'm not sure about here is that we use sg_alloc_table_from_pages_segment(), but we actually don't pass the max segment size (as returned by dma_get_max_seg_size()) to it. I'm also not exactly sure what's the difference between "max mapping size" and "max seg size". +Robin Murphy +Christoph Hellwig I think we could benefit from your expertise here. Generally looking at videobuf2-dma-sg, I feel like we would benefit from some kind of dma_alloc_table_from_pages() that simply takes the struct dev pointer and does everything necessary. Best regards, Tomasz
