int do_probe (ide_drive_t * drive, u8 cmd);
do_probe has the difficult job of finding a drive if it exists, without getting hung up if it doesn't exist, without trampling on ethernet cards, and without leaving any IRQs dangling to haunt us later.
If a drive is ``known'' to exist (from CMOS or kernel parameters), but does not respond right away, the probe will ``hang in there'' for the maximum wait time (about 30 seconds), otherwise it will exit much more quickly.
0 device was identified 1 device timed-out (no response to identify request) 2 device aborted the command (refused to identify itself) 3 bad status from device (possible for ATAPI drives) 4 probe was not attempted because failure was obvious