介紹

PetaLinux 能夠根據Vivado的設計，自動生成V4L2的Video Pipeline的devicetree。但是它主要為Xilinx的VCU TRD服務，測試的組合比較少。很多時候，需要根據自己的工程，修改V4L2的Video Pipeline的devicetree。

硬件設計

有項目需要對輸入的視頻，既需要對原始視頻做編解碼，也需要縮放后再做編解碼。于是創建了下面的硬件設計。

axis_data_fifo主要用于暫時緩存數據。axis_broadcaster和vpss之間的axis_data_fifo、axis_register_slice，可以刪除，完全不影響共。

兩個framebuffer_write的tready通過邏輯門的“或”操作，連接到了一起，再連接到前級axis_register_slice的輸入，保證只要有一個framebuffer_write在工作，前面的模塊就能向后輸出數據。

devicetree

對于上述的硬件設計，對應的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標簽名稱。

v_proc_ss的devicetree里，port@0是輸入；port@1是輸出。

broadcaster的devicetree里，port@0是輸入；port@1和port@2是輸出。

另外，V4L2的設備號，根據“xlnx，video”設備里的port順序分配。 如果port@0在port@1后面，那么port@0也會被分配video1; 而port@1也會被分配video0.

審核編輯：郭婷