• Tejun Heo's avatar
    libata: implement and use ops inheritance · 029cfd6b
    Tejun Heo authored
    libata lets low level drivers build ata_port_operations table and
    register it with libata core layer.  This allows low level drivers
    high level of flexibility but also burdens them with lots of
    boilerplate entries.
    
    This becomes worse for drivers which support related similar
    controllers which differ slightly.  They share most of the operations
    except for a few.  However, the driver still needs to list all
    operations for each variant.  This results in large number of
    duplicate entries, which is not only inefficient but also error-prone
    as it becomes very difficult to tell what the actual differences are.
    
    This duplicate boilerplates all over the low level drivers also make
    updating the core layer exteremely difficult and error-prone.  When
    compounded with multi-branched development model, it ends up
    accumulating inconsistencies over time.  Some of those inconsistencies
    cause immediate problems and fixed.  Others just remain there dormant
    making maintenance increasingly difficult.
    
    To rectify the problem, this patch implements ata_port_operations
    inheritance.  To allow LLDs to easily re-use their own ops tables
    overriding only specific methods, this patch implements poor man's
    class inheritance.  An ops table has ->inherits field which can be set
    to any ops table as long as it doesn't create a loop.  When the host
    is started, the inheritance chain is followed and any operation which
    isn't specified is taken from the nearest ancestor which has it
    specified.  This operation is called finalization and done only once
    per an ops table and the LLD doesn't have to do anything special about
    it other than making the ops table non-const such that libata can
    update it.
    
    libata provides four base ops tables lower drivers can inherit from -
    base, sata, pmp, sff and bmdma.  To avoid overriding these ops
    accidentaly, these ops are declared const and LLDs should always
    inherit these instead of using them directly.
    
    After finalization, all the ops table are identical before and after
    the patch except for setting .irq_handler to ata_interrupt in drivers
    which didn't use to.  The .irq_handler doesn't have any actual effect
    and the field will soon be removed by later patch.
    
    * sata_sx4 is still using old style EH and currently doesn't take
      advantage of ops inheritance.
    Signed-off-by: default avatarTejun Heo <htejun@gmail.com>
    029cfd6b
ahci.c 62.4 KB