Hi Tomasz, On 12/15/20 1:47 PM, Tomasz Figa wrote: > On Tue, Dec 15, 2020 at 8:16 PM Stanimir Varbanov > <stanimir.varbanov@xxxxxxxxxx> wrote: >> >> Hi, >> >> Cc: Robin >> >> On 12/14/20 2:57 PM, Alexandre Courbot wrote: >>> This driver uses the SG vb2 ops, but effectively only ever accesses the >>> first entry of the SG table, indicating that it expects a flat layout. >>> Switch it to use the contiguous ops to make sure this expected invariant >> >> Under what circumstances the sg table will has nents > 1? I came down to >> [1] but not sure I got it right. >> >> I'm afraid that for systems with low amount of system memory and when >> the memory become fragmented, the driver will not work. That's why I >> started with sg allocator. > > It is exactly the opposite. The vb2-dma-contig allocator is "contig" > in terms of the DMA (aka IOVA) address space. In other words, it > guarantees that having one DMA address and length fully describes the Ahh, I missed that part. Looks like I misunderstood videobu2 contig allocator. > buffer. This seems to be the requirement of the hardware/firmware > handled by the venus driver. If the device is behind an IOMMU, which > is the case for the SoCs in question, the underlying DMA ops will > actually allocate a discontiguous set of pages, so it has nothing to > do to system memory amount or fragmentation. If for some reason the > IOMMU can't be used, there is no way around, the memory needs to be > contiguous because of the hardware/firmware/driver expectation. > > On the other hand, the vb2-dma-sg allocator doesn't have any > continuity guarantees for the DMA, or any other, address space. The > current code works fine, because it calls dma_map_sg() on the whole > set of pages and that ends up mapping it contiguously in the IOVA > space, but that's just an implementation detail, not an API guarantee. It was good to know. Thanks for the explanation. > > Best regards, > Tomasz > >> >> [1] >> https://elixir.bootlin.com/linux/v5.10.1/source/drivers/iommu/dma-iommu.c#L782 >> >>> is always enforced. Since the device is supposed to be behind an IOMMU >>> this should have little to none practical consequences beyond making the >>> driver not rely on a particular behavior of the SG implementation. >>> >>> Reported-by: Tomasz Figa <tfiga@xxxxxxxxxxxx> >>> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxxxx> >>> --- >>> Hi everyone, >>> >>> It probably doesn't hurt to fix this issue before some actual issue happens. >>> I have tested this patch on Chrome OS and playback was just as fine as with >>> the SG ops. >>> >>> drivers/media/platform/Kconfig | 2 +- >>> drivers/media/platform/qcom/venus/helpers.c | 9 ++------- >>> drivers/media/platform/qcom/venus/vdec.c | 6 +++--- >>> drivers/media/platform/qcom/venus/venc.c | 6 +++--- >>> 4 files changed, 9 insertions(+), 14 deletions(-) >>> >>> diff --git a/drivers/media/platform/Kconfig b/drivers/media/platform/Kconfig >>> index 35a18d388f3f..d9d7954111f2 100644 >>> --- a/drivers/media/platform/Kconfig >>> +++ b/drivers/media/platform/Kconfig >>> @@ -533,7 +533,7 @@ config VIDEO_QCOM_VENUS >>> depends on INTERCONNECT || !INTERCONNECT >>> select QCOM_MDT_LOADER if ARCH_QCOM >>> select QCOM_SCM if ARCH_QCOM >>> - select VIDEOBUF2_DMA_SG >>> + select VIDEOBUF2_DMA_CONTIG >>> select V4L2_MEM2MEM_DEV >>> help >>> This is a V4L2 driver for Qualcomm Venus video accelerator >>> diff --git a/drivers/media/platform/qcom/venus/helpers.c b/drivers/media/platform/qcom/venus/helpers.c >>> index 50439eb1ffea..859d260f002b 100644 >>> --- a/drivers/media/platform/qcom/venus/helpers.c >>> +++ b/drivers/media/platform/qcom/venus/helpers.c >>> @@ -7,7 +7,7 @@ >>> #include <linux/mutex.h> >>> #include <linux/slab.h> >>> #include <linux/kernel.h> >>> -#include <media/videobuf2-dma-sg.h> >>> +#include <media/videobuf2-dma-contig.h> >>> #include <media/v4l2-mem2mem.h> >>> #include <asm/div64.h> >>> >>> @@ -1284,14 +1284,9 @@ int venus_helper_vb2_buf_init(struct vb2_buffer *vb) >>> struct venus_inst *inst = vb2_get_drv_priv(vb->vb2_queue); >>> struct vb2_v4l2_buffer *vbuf = to_vb2_v4l2_buffer(vb); >>> struct venus_buffer *buf = to_venus_buffer(vbuf); >>> - struct sg_table *sgt; >>> - >>> - sgt = vb2_dma_sg_plane_desc(vb, 0); >>> - if (!sgt) >>> - return -EFAULT; >>> >>> buf->size = vb2_plane_size(vb, 0); >>> - buf->dma_addr = sg_dma_address(sgt->sgl); >> >> Can we do it: >> >> if (WARN_ON(sgt->nents > 1)) >> return -EFAULT; >> >> I understand that logically using dma-sg when the flat layout is >> expected by the hardware is wrong, but I haven't seen issues until now. >> >>> + buf->dma_addr = vb2_dma_contig_plane_dma_addr(vb, 0); >>> >>> if (vb->type == V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE) >>> list_add_tail(&buf->reg_list, &inst->registeredbufs); >>> diff --git a/drivers/media/platform/qcom/venus/vdec.c b/drivers/media/platform/qcom/venus/vdec.c >>> index 8488411204c3..3fb277c81aca 100644 >>> --- a/drivers/media/platform/qcom/venus/vdec.c >>> +++ b/drivers/media/platform/qcom/venus/vdec.c >>> @@ -13,7 +13,7 @@ >>> #include <media/v4l2-event.h> >>> #include <media/v4l2-ctrls.h> >>> #include <media/v4l2-mem2mem.h> >>> -#include <media/videobuf2-dma-sg.h> >>> +#include <media/videobuf2-dma-contig.h> >>> >>> #include "hfi_venus_io.h" >>> #include "hfi_parser.h" >>> @@ -1461,7 +1461,7 @@ static int m2m_queue_init(void *priv, struct vb2_queue *src_vq, >>> src_vq->io_modes = VB2_MMAP | VB2_DMABUF; >>> src_vq->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY; >>> src_vq->ops = &vdec_vb2_ops; >>> - src_vq->mem_ops = &vb2_dma_sg_memops; >>> + src_vq->mem_ops = &vb2_dma_contig_memops; >>> src_vq->drv_priv = inst; >>> src_vq->buf_struct_size = sizeof(struct venus_buffer); >>> src_vq->allow_zero_bytesused = 1; >>> @@ -1475,7 +1475,7 @@ static int m2m_queue_init(void *priv, struct vb2_queue *src_vq, >>> dst_vq->io_modes = VB2_MMAP | VB2_DMABUF; >>> dst_vq->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY; >>> dst_vq->ops = &vdec_vb2_ops; >>> - dst_vq->mem_ops = &vb2_dma_sg_memops; >>> + dst_vq->mem_ops = &vb2_dma_contig_memops; >>> dst_vq->drv_priv = inst; >>> dst_vq->buf_struct_size = sizeof(struct venus_buffer); >>> dst_vq->allow_zero_bytesused = 1; >>> diff --git a/drivers/media/platform/qcom/venus/venc.c b/drivers/media/platform/qcom/venus/venc.c >>> index 1c61602c5de1..a09550cd1dba 100644 >>> --- a/drivers/media/platform/qcom/venus/venc.c >>> +++ b/drivers/media/platform/qcom/venus/venc.c >>> @@ -10,7 +10,7 @@ >>> #include <linux/pm_runtime.h> >>> #include <linux/slab.h> >>> #include <media/v4l2-mem2mem.h> >>> -#include <media/videobuf2-dma-sg.h> >>> +#include <media/videobuf2-dma-contig.h> >>> #include <media/v4l2-ioctl.h> >>> #include <media/v4l2-event.h> >>> #include <media/v4l2-ctrls.h> >>> @@ -1001,7 +1001,7 @@ static int m2m_queue_init(void *priv, struct vb2_queue *src_vq, >>> src_vq->io_modes = VB2_MMAP | VB2_USERPTR | VB2_DMABUF; >>> src_vq->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY; >>> src_vq->ops = &venc_vb2_ops; >>> - src_vq->mem_ops = &vb2_dma_sg_memops; >>> + src_vq->mem_ops = &vb2_dma_contig_memops; >>> src_vq->drv_priv = inst; >>> src_vq->buf_struct_size = sizeof(struct venus_buffer); >>> src_vq->allow_zero_bytesused = 1; >>> @@ -1017,7 +1017,7 @@ static int m2m_queue_init(void *priv, struct vb2_queue *src_vq, >>> dst_vq->io_modes = VB2_MMAP | VB2_USERPTR | VB2_DMABUF; >>> dst_vq->timestamp_flags = V4L2_BUF_FLAG_TIMESTAMP_COPY; >>> dst_vq->ops = &venc_vb2_ops; >>> - dst_vq->mem_ops = &vb2_dma_sg_memops; >>> + dst_vq->mem_ops = &vb2_dma_contig_memops; >>> dst_vq->drv_priv = inst; >>> dst_vq->buf_struct_size = sizeof(struct venus_buffer); >>> dst_vq->allow_zero_bytesused = 1; >>> >> >> -- >> regards, >> Stan -- regards, Stan
