BeagleBone Black hdmi audio

For simple use,I have a audio supported display(1280x720) connecting to BBB with hdmi,when I run ./ | grep UBOOT,it shows Loaded Overlay:[];when I run aplay -l,it shows card 0:Black [TI BeagleBone Black],device 0:davinci-mcasp.0-i2s-hifi…,so I think the dtb is OK,but alsamixer only shows Card: TI BeagleBone Black This sound device does not have any control. and as the picture below figures outBBB audio play

there’s no sound heard from my display.I have tried some way but none of them worked ,what’s wrong with my BBB hdmi audio or with my operation?My kernel is Linux beaglebone 4.19.94-ti-r71 #1buster SMP PREEMPT armv7l