• Takashi Sakamoto's avatar
    ALSA: dice: postpone card registration · b59fb190
    Takashi Sakamoto authored
    Some models based on ASIC for Dice II series (STD, CP) change their
    hardware configurations after appearing on IEEE 1394 bus. This is due to
    interactions of boot loader (RedBoot), firmwares (eCos) and vendor's
    configurations. This causes current ALSA dice driver to get wrong
    information about the hardware's capability because its probe function
    runs just after detecting unit of the model.
    
    As long as I investigated, it takes a bit time (less than 1 second) to load
    the firmware after bootstrap. Just after loaded, the driver can get
    information about the unit. Then the hardware is initialized according to
    vendor's configurations. After, the got information becomes wrong.
    Between bootstrap, firmware loading and post configuration, some bus resets
    are observed.
    
    This commit offloads most processing of probe function into workqueue and
    schedules the workqueue after successive bus resets. This has an effect to
    get correct hardware information and avoid involvement to bus reset storm.
    
    For code simplicity, this change effects all of Dice-based models, i.e.
    Dice II, Dice Jr., Dice Mini and Dice III.
    
    I use a loose strategy to manage a race condition between the work and the
    bus reset. This is due to a specification of dice transaction. When bus
    reset occurs, registered address for the transaction is cleared. Drivers
    must re-register their own address again. While, this operation is required
    for the work because the work includes to wait for the transaction. This
    commit uses no lock primitives for the race condition. Instead, checking
    'registered' member of 'struct snd_dice' avoid executing the work again.
    If sound card is not registered, the work can be scheduled again by bus
    reset handler.
    
    When .remove callback is executed, the sound card is going to be released.
    The work should not be pending or executed in the releasing. This commit
    uses cancel_delayed_work_sync() in .remove callback and wait till the
    pending work finished. After .remove callback, .update callback is not
    executed, therefore no works are scheduled again.
    Signed-off-by: default avatarTakashi Sakamoto <o-takashi@sakamocchi.jp>
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    b59fb190
dice.c 8.99 KB