What is a valid link in the media controller?

Question

I have the device tree entries below. When I query the entries i my /dev/media0 I get
Desc 0: video_cap output 0 with pads: 1 links: 0
Desc 1: video_cap input 1 with pads: 1 links: 1
Desc 2: 43c40000.switch with pads: 3 links: 0
Desc 3: 43c20000.tpg with pads: 1 links: 1
Why are some of the links 0? In particular, I think the "video_cap output 0" is connected to the tpg and that seems it should be 1? Or, is the "video_cap input 1" connected to the tpg? I can't really make sense of what input/output refers to in respect to what that means for the xlnx,video node.
tpg@43c20000 {
compatible = "xlnx,v-tpg-6.0", "xlnx,v-tpg-5.0";
reg = <0x43c20000 0x10000>;
clocks = <0x2 15>;
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
reg = <0>;
xlnx,video-format = <0>;
xlnx,video-width = <8>;
tpgout: endpoint {
remote-endpoint = <&videocapin>;
switch@43c40000 {
compatible = "xlnx,v-switch-1.0";
reg = <0x43c40000 0x10000>;
clocks = <0x2 15>;
#xlnx,inputs = <1>;
#xlnx,outputs = <2>;
ports {
#address-cells = <1>;
#size-cells = <0>;
port@0 {
reg = <0>;
switchin0: endpoint {
remote-endpoint = <&videocapout>;
video_cap {
compatible = "xlnx,video";
dmas = <0xc 0x1>, <0xc 0x0>;
dma-names = "port0", "port1";
ports {
#address-cells = <0x1>;
#size-cells = <0x0>;
port@0 {
reg = <0x0>;
direction = "input";
videocapin: endpoint {
remote-endpoint = <&tpgout>;
port@1 {
reg = <0x1>;
direction = "output";
videocapout: endpoint {
remote-endpoint = <&switchin0>;
axivdma@43000000 {
compatible = "xlnx,axi-vdma-1.00.a";
reg = <0x43000000 0x10000>;
xlnx,flush-fsync = <0x1>;
xlnx,num-fstores = <0x3>;
#dma-cells = <0x1>;
linux,phandle = <0xc>;
phandle = <0xc>;
dma-channel@43000000 {
compatible = "xlnx,axi-vdma-mm2s-channel";
interrupt-parent = <0x3>;
interrupts = <0 90 4>;
xlnx,datawidth = <0x10>;
dma-channel@43000030 {
compatible = "xlnx,axi-vdma-s2mm-channel";
interrupt-parent = <0x3>;
interrupts = <0 91 4>;
xlnx,datawidth = <0x10>;
};

Answer 1

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OT