On Wed, Dec 16, 2020 at 4:21 AM Nicolas Dufresne <nicolas@xxxxxxxxxxxx> wrote: > > Le mardi 15 décembre 2020 à 15:54 +0200, Stanimir Varbanov a écrit : > > 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. > > I'm learning everyday too, but I'm surprised I don't see a call to > vb2_dma_contig_set_max_seg_size() in this driver (I could also just have missed > a patch when overlooking this thread) ? > > The reason I'm asking, doc says it should be called by driver supporting IOMMU, > which seems to be the case for such drivers (MFC, exynos4-is, exynos-gsc, mtk- > mdp, s5p-g2d, hantro, rkvdec, zoran, ti-vpe, ..). I posting it, worst case it's > all covered and we are good, otherwise perhaps a downstream patch didn't make it > ? > > /** > * 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. > */ It does call dma_set_max_seg_size() directly: https://elixir.bootlin.com/linux/latest/source/drivers/media/platform/qcom/venus/core.c#L230 Actually, why do we even need a vb2 helper for this? > > regards, > Nicolas > > > > > > 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 > > > >
