修改V4L2的Video Pipeline的devicetree

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.

审核编辑：郭婷