AFD is in use

$ asmcmd afd_state ASMCMD-9526: The AFD state is 'LOADED' and filtering is 'ENABLED' on host 'ora192rac02.jks.com'

AFD is NOT in use

[grid@ora12102b ~]$ asmcmd afd_state
ASMCMD-9526: The AFD state is 'NOT INSTALLED' and filtering is 'DEFAULT' on host 'ora12102b.jks.com'

or

$ asmcmd afd_state
ASMCMD-9530: The AFD state is 'NOT SUPPORTED'

It is possible to just use udev

AFD is not installed

[grid@ora12102b ~]$ asmcmd afd_state
ASMCMD-9526: The AFD state is 'NOT INSTALLED' and filtering is 'DEFAULT' on host 'ora12102b.jks.com'

oracleasm does not know about disks - there is no output

[grid@ora12102b ~]$
[grid@ora12102b ~]$ oracleasm listdisks

Just use asm lsdsk

$ asmcmd lsdsk  --suppressheader
/dev/asm01