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alsa -l devicetree overlay rpi rev 2

>I am trying to wade my way through the device tree concept.

>I have found on my platform that if I use a device tree overlay file for a particular sound module then perform the following on the command line:


    "aplay -l"




>Alsa reports the sound card I'm looking for.


>Additionally, if I perform:


    "sudo modprobe -r snd_soc_hifiberry_dac.ko"
    "sudo alsa force-reload"
    "aplay -l"




>Alsa no longer reports the sound card and this makes sense to me.


>I can even go one step further and do:


    "sudo modprobe snd_soc_hifiberry_dac.ko"
    "sudo alsa force-reload"
    "aplay -l"



>Alsa reports the sound card I'm looking for again.


>However, if I remove the overlay file entry from /boot/config.txt, reboot the system and perform the following:


    "sudo modprobe snd_soc_hifiberry_dac.ko"
    "sudo alsa force-reload"
    "aplay -l"




>Alsa does not report the sound card.


>My question is, what is the overlay file doing that I am obviously missing when trying to modprobe without the overlay file? I'd really like to use modprobe without the need for the overlay file. Can anyone tell me what is going on?

thanks in advance.

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