【工程师分享】修改V4L2的Video Pipeline的devicetree

作者:HankFu,本文转载自:博客园

介绍
PetaLinux 能够根据Vivado的设计,自动生成V4L2的Video Pipeline的devicetree。但是它主要为Xilinx的VCU TRD服务,测试的组合比较少。很多时候,需要根据自己的工程,修改V4L2的Video Pipeline的devicetree。

硬件设计
有项目需要对输入的视频,既需要对原始视频做编解码,也需要缩放后再做编解码。于是创建了下面的硬件设计。

axis_data_fifo主要用于暂时缓存数据。axis_broadcaster和vpss之间的axis_data_fifo、axis_register_slice,可以删除,完全不影响共。

两个framebuffer_write的tready通过逻辑门的“或”操作,连接到了一起,再连接到前级axis_register_slice的输入,保证只要有一个framebuffer_write在工作,前面的模块就能向后输出数据。

devicetree
对于上述的硬件设计,对应的V4L2的devicetree如下:

&amba_pl {

/delete-node/ axis_broadcasterhdmi_input_axis_broadcaster_0@0;

/* media-ctl prints out each node name of the video pipeline.
hdmi_brdcst_0@0: media-ctl prints it out. */
hdmi_brdcst_0_lb: hdmi_brdcst_0@0 {
compatible = "xlnx,axis-broadcaster-1.1";

hdmi_brdcst_0_ports: ports {
#address-cells = ;
#size-cells = ;
};
};

/delete-node/ vcapaxis_broad_out1hdmi_input_axis_broadcaster_0;
/delete-node/ vcap_hdmi_input_v_proc_ss_0;

/* vcap_hdmi_brdcst_0: media-ctl prints it out. */
vcap_hdmi_brdcst_0 {
compatible = "xlnx,video";
dma-names = "port0", "port1";
dmas = , ;

/* vcap_hdmi_brdcst_0_ports: Linux prints it out in log. */
vcap_hdmi_brdcst_0_ports: ports {
#address-cells = ;
#size-cells = ;

vcap_broadcaster_0_port1: port@0 {
direction = "input";
reg = ;
/* Video input pipeline 1:
hdmi_rx_ss --> broadcaster_0 : 1 --> v_proc_ss_0 --> v_frmbuf_wr_1
hdmi_rx_ss : source_to_axis_broad_in0_from_v_hdmi_rx_ss_0
broadcaster_0 : out 1 : port2 :: src_to_vpss0_from_broad_port2_hwout1
v_proc_ss_0 @a0040000 port@0 :: sink_to_vpss0_from_broad_port2_hwout1
v_proc_ss_0 @a0040000 port@1 :: src_to_frmbuf_wr1_from_vpss_0
v_frmbuf_wr_1 @a0080000 :: hdmi_input_v_frmbuf_wr_1
*/
sink_to_frmbuf_wr1_from_vpss_0: endpoint {
remote-endpoint = ;
};
};

vcap_broadcaster_0_port2: port@1 {
direction = "input";
reg = ;
/* Video input pipeline 0:
hdmi_rx_ss --> broadcaster_0 : 0 --> v_frmbuf_wr_0
hdmi_rx_ss : source_to_axis_broad_in0_from_v_hdmi_rx_ss_0
broadcaster_0 : out 0 : port1 :: src_to_frmbuf_wr0_from_broad_port1_hwout0
v_frmbuf_wr_1 @a0010000 :: hdmi_input_v_frmbuf_wr_0
hdmi_input_ v_frmbuf_wr_0 hdmi_input_ axis_broadcaster_0
*/
sink_to_frmbuf_wr0_from_broad_port1_hwout0: endpoint {
remote-endpoint = ;
};
};

};
};
};

/* hdmi_input_v_hdmi_rx_ss_0: v_hdmi_rx_ss@a0000000 */
&hdmirx_porthdmi_input_v_hdmi_rx_ss_0 {
source_to_axis_broad_in0_from_v_hdmi_rx_ss_0: endpoint {
remote-endpoint = ;
};
};

&hdmi_brdcst_0_ports{

/delete-node/ axis_broad_port1hdmi_input_axis_broadcaster_0;
/delete-node/ axis_broad_port2hdmi_input_axis_broadcaster_0;
/delete-node/ axis_broad_port0hdmi_input_axis_broadcaster_0;

axis_broad_port1_hw_output0: port@1 {
reg = ;
src_to_frmbuf_wr0_from_broad_port1_hwout0: endpoint {
remote-endpoint = ;
};
};
axis_broad_port2_hw_output1: port@2 {
reg = ;
src_to_vpss0_from_broad_port2_hwout1: endpoint {
remote-endpoint = ;
};
};
axis_broad_port0_hw_input: port@0 {
reg = ;
sink_to_broad_in0__from_v_hdmi_rx_ss_0: endpoint {
remote-endpoint = ;
};
};
};

&scaler_portshdmi_input_v_proc_ss_0{

/delete-node/ port@0;
/delete-node/ port@1;

scaler_port1_v_proc_ss_0: port@1 {
/* For xlnx,video-format user needs to fill as per their requirement */
reg = ;
xlnx,video-format = ;
xlnx,video-width = ;
src_to_frmbuf_wr1_from_vpss_0: endpoint {
remote-endpoint = ;
};
};
scaler_port0_v_proc_ss_0: port@0 {
/* For xlnx,video-format user needs to fill as per their requirement */
reg = ;
xlnx,video-format = ;
xlnx,video-width = ;
sink_to_vpss0_from_broad_port2_hwout1: endpoint {
remote-endpoint = ;
};
};
};

上述的devicetree,使用了更短更好理解的标签名称。

v_proc_ss的devicetree里,port@0是输入;port@1是输出。
broadcaster的devicetree里,port@0是输入;port@1和port@2是输出。

另外,V4L2的设备号,根据"xlnx,video"设备里的port顺序分配。 如果port@0在port@1后面,那么port@0也会被分配video1; 而port@1也会被分配video0.

测试环境
PetaLinux 2020.2
Linux 5.4.0
ZCU106

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