• Stefan Richter's avatar
    ieee1394: sbp2: safer last_orb and next_ORB handling · cc078189
    Stefan Richter authored
    The sbp2 initiator has two ways to tell a target's fetch agent about new
    command ORBs:
     - Write the ORB's address to the ORB_POINTER register.  This must not
       be done while the fetch agent is active.
     - Put the ORB's address into the previously submitted ORB's next_ORB
       field and write to the DOORBELL register.  This may be done while the
       fetch agent is active or suspended.  It must not be done while the
       fetch agent is in reset state.
    Sbp2 has a last_orb pointer which indicates in what way a new command
    should be announced.  That pointer is concurrently accessed at various
    occasions.  Furthermore, initiator and target are accessing the next_ORB
    field of ORBs concurrently and asynchronously.
    
    This patch does:
     - Protect all initiator accesses to last_orb by sbp2_command_orb_lock.
     - Add pci_dma_sync_single_for_device before a previously submitted
       ORB's next_ORB field is overwritten.
     - Insert a memory barrier between when next_ORB_lo and next_ORB_hi are
       overwritten.  Next_ORB_hi must not be updated before next_ORB_lo.
     - Remove the rather unspecific and now superfluous qualifier "volatile"
       from the next_ORB fields.
     - Add comments on how last_orb is connected with what is known about
       the target's fetch agent's state.
    Signed-off-by: default avatarStefan Richter <stefanr@s5r6.in-berlin.de>
    cc078189
sbp2.h 12.8 KB