Comment 74 for bug 871808

http://git.alsa-project.org/?p=alsa-lib.git;a=blob_plain;f=test/chmap.c;hb=HEAD

chmap -Dhw:0 query

do you mean that you expect only notebook only support 2 ch by default

 4 ch is only supported when subwoofer is plugged

does the user manual mention that the subwoofer can be plugged (hot- plug0 after the notebooke is power on