Video Buffer Management in NVIDIA Jetson Xavier NX

Robotics & Edge Computing Jetson & Embedded Systems Jetson Xavier NX
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Hi,

I’m trying to manage(view and manipulate) the captured RAW Frames at the kernel level. So I found videobuf2 in the default kernel sources(4.9.x) to manage buffers for v4l2 drivers. So Is there any similar alternative available for NVIDIA sources?. If any, can you suggest me a reference for the same?. Please note that I wanted to perform this operation at the kernel level only, not at the userspace end.

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Current Jetson camera framework using vb2, suppose vb2 could be the good choose.

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Hi @ShaneCCC

Thanks for your reply!
I was referring to the below structures to extract the video buffer at the kernel level.

struct vb2_buffer
struct vb2_v4l2_buffer
struct tegra_channel
struct tegra_channel_buffer

But I’m not able to get the pixel data from video buffer. Instead, I got some properties like number of planes and image size.

Can you help to find it out?

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Check the vi5_setup_surface() in vi5_fops.c the surface[0].base_address

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Hi @ShaneCCC ,

I cannot find surface[0].base_address. Only found offset and offset_hi. I wanted to read out pixels from a specified locations from the entire buffer.

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I mean the “desc_memoryinfo->surface[0].base_address = offset”

static void vi5_setup_surface(struct tegra_channel *chan,
        struct tegra_channel_buffer *buf, unsigned int descr_index, unsigned int vi_port)
{
        dma_addr_t offset = buf->addr + chan->buffer_offset[vi_port];
        u32 height = chan->format.height;
        u32 width = chan->format.width;
        u32 format = chan->fmtinfo->img_fmt;
        u32 bpl = chan->format.bytesperline;
        u32 data_type = chan->fmtinfo->img_dt;
        u32 nvcsi_stream = chan->port[vi_port];
        struct capture_descriptor *desc = &chan->request[vi_port][descr_index];
        struct capture_descriptor_memoryinfo *desc_memoryinfo =
                &chan->tegra_vi_channel[vi_port]->capture_data->requests_memoryinfo[descr_index];

        if (chan->valid_ports > NVCSI_STREAM_1){
                height = chan->gang_height;
                width = chan->gang_width;
                offset = buf->addr + chan->buffer_offset[1 - vi_port];
        }

        memcpy(desc, &capture_template, sizeof(capture_template));
        memset(desc_memoryinfo, 0, sizeof(*desc_memoryinfo));

        desc->sequence = chan->capture_descr_sequence;
        desc->ch_cfg.match.stream = (1u << nvcsi_stream); /* one-hot bit encoding */
        desc->ch_cfg.match.vc = (1u << chan->virtual_channel); /* one-hot bit encoding */
        desc->ch_cfg.frame.frame_x = width;
        desc->ch_cfg.frame.frame_y = height;
        desc->ch_cfg.match.datatype = data_type;
        desc->ch_cfg.match.datatype_mask = 0x3f;
        desc->ch_cfg.pixfmt_enable = 1;
        desc->ch_cfg.pixfmt.format = format;

        desc_memoryinfo->surface[0].base_address = offset;
        desc_memoryinfo->surface[0].size = chan->format.bytesperline * height;
        desc->ch_cfg.atomp.surface_stride[0] = bpl;
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Hi @ShaneCCC

Thank you for the response.

I was asking about that is there any way to view each of the pixel’s value(or view the entire v4l2 buffer) at kernel side?.

I was referring to vb2_queue, vb2_plane, vb2_v4l_buffer and tegra_channel structures to locate the exact buffer from where I could find the data.

Also, I’m using Jetpack 4.4.1 (Kernel 4.9.140).

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The offset of dma_addr_t should be the buffer start address for pixel data.

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Hi @ShaneCCC

So you’re suggesting me to access the buffer using this starting address, right?. I tried to do that by incrementing the position by 1 and print is using printk, but giving 0 values. Am I doing anything wrong?

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OK, maybe you can reference to the user space APP like v4l2-ctl to query the buffer.

Thanks

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