linux kernel version Linux version 4.14.98-imx_4.14.98_2.0.0_ga+g5d6cbeafb80c.
the boot log about hdmi:
root@imx8mqevk:~# dmesg | grep hdmi
[ 4.028982] imx-spdif sound-hdmi-arc: snd-soc-dummy-dai <-> 308a0000.spdif mapping ok
[ 4.036839] imx-spdif sound-hdmi-arc: ASoC: no DMI vendor name!
[ 4.108431] imx-cdnhdmi sound-hdmi: ASoC: CODEC DAI i2s-hifi not registered
[ 4.115468] imx-cdnhdmi sound-hdmi: snd_soc_register_card failed (-517)
[ 4.806502] imx-cdnhdmi sound-hdmi: ASoC: CODEC DAI i2s-hifi not registered
[ 4.813554] imx-cdnhdmi sound-hdmi: snd_soc_register_card failed (-517)
[ 4.857804] #2: imx-hdmi-arc
root@imx8mqevk:~# dmesg | grep dcss
[ 1.009618] dcss-core 32e00000.dcss: failed to get pix clock
[ 1.015299] dcss-core 32e00000.dcss: clocks initialization failed
[ 1.021413] dcss-core: probe of 32e00000.dcss failed with error -2