Messages in this thread | | | Subject | Re: [PATCH] media: venus: use contig vb2 ops | From | Robin Murphy <> | Date | Tue, 15 Dec 2020 11:34:34 +0000 |
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On 2020-12-15 11:16, Stanimir Varbanov 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.
Despite what videobuf-dma-contig seems to assume, dma_alloc_coherent() makes no guarantee of providing physically contiguous memory. What it provides is *DMA contiguous* memory, i.e. from the point of view of the device. When an IOMMU is present and managed by the DMA API, such buffers may be assembled out of physically-scattered pages (particularly under memory pressure/fragmentation).
Robin.
> > [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@chromium.org> >> Signed-off-by: Alexandre Courbot <acourbot@chromium.org> >> --- >> 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; >> >
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