HDD power states + kernel

[Mukesh Rajan]

hi,

i need to implement powering down of the Hard Disk in the linux kernel. i
understand that using "hdparm" i could set a timeout and power down the
HDD after a certain idle time.

but then HDD has 4 power states and instead of powering down to the lowest
power state, i would like to power down one state at a time based on
certain timeout values.  

i'm not sure where to start with this. would i have to play around with
"llrwblk.c"? and what would i have to do here in order to monitor disk
inactivity (idleness)? or should i look into APM stuff?

any help or pointers in this direction would be of great help.

thanks in advance,
mukesh