[SCSI] aha152x: preliminary fixes and some comments

[SCSI] aha152x: preliminary fixes and some comments

  hunk by hunk:
  - CHECK_CONDITION is what happens to cmnd->status >> 1
    or after status_byte() macro. But here it is used
    directly on status which means 0x1 which is an undefined
    bit in the standard. And is a status that will never
    return from a target.

  - in busfree_run at the DONE_SC phase we have 3 distinct
    operation:
	1-if(DONE_SC->SCp.phase & check_condition)
          The REQUEST_SENSE command return.
          - Restore original command
	  - Than continue to operation 3.
	2-if(DONE_SC->SCp.Status==SAM_STAT_CHECK_CONDITION)
          A regular command returned with a status.
	  - Internally re-Q a REQUEST_SENSE.
	  - Do not do operation 3.
	3-
	  - Complete the command and return it to scsi-ml
     So the 0x2 in both these operations (1,2) means the scsi
     check-condition status, hence SAM_STAT_CHECK_CONDITION

  - Here the code asks about !(DONE_SC->SCp.Status & not_issued)
    but "not_issued" is an enum belonging to the "phase" member
    and not to the Status returned from target. The reason this
    works is because not_issued==1 and Also CHECK_CONDITION==1
    (remember from hunk 1). So actually the code was asking
    !(DONE_SC->SCp.Status & CHECK_CONDITION). Which means
    "Has the status been read from target yet?"
    Staus is read at status_run(). "not_issued" is
    cleared in seldo_run() which is usually earlier than
    status_run().

  So this patch does nothing as far as assembly is concerned
  but it does let the reader understand what is going on.

Signed-off-by: Boaz Harrosh <bharrosh@panasas.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>