From L5.4 BSP, the iMX8QM HDMI RX feature is removed from BSP, but it is added back in L5.10.52 2.1.0 BSP. The followed is the detail steps to use HDMI RX.
CONFIG_IMX8_MEDIA_DEVICE=y
CONFIG_MHDP_HDMIRX=y
gst-launch-1.0 v4l2src device=/dev/video2 ! autovideosink
Note: To test the hdmi feature, the display should also use the HDMI TX. And in Uboot, to load the hdmirx firmware, we can run the followed commands first, then run the "boot" command:
run loadhdprx
hdprx load 0x9c800000
setenv fdt_file imx8qm-mek-hdmi-rx.dtb