1. NAME▲
ata_xfer_mode2shift - Find matching xfer_shift for XFER_*
2. SYNOPSIS ▲
int ata_xfer_mode2shift(unsigned long xfer_mode );
3. ARGUMENTS ▲
xfer_mode
    XFER_* of interest
4. DESCRIPTION ▲
Return matching xfer_shift for xfer_mode.
5. LOCKING ▲
None.
6. RETURNS ▲
Matching xfer_shift, -1 if no match found.
7. AUTHOR ▲
Jeff Garzik
    Author.
8. COPYRIGHT ▲