• Dan Williams's avatar
    dmaengine, async_tx: add a "no channel switch" allocator · 138f4c35
    Dan Williams authored
    Channel switching is problematic for some dmaengine drivers as the
    architecture precludes separating the ->prep from ->submit.  In these
    cases the driver can select ASYNC_TX_DISABLE_CHANNEL_SWITCH to modify
    the async_tx allocator to only return channels that support all of the
    required asynchronous operations.
    
    For example MD_RAID456=y selects support for asynchronous xor, xor
    validate, pq, pq validate, and memcpy.  When
    ASYNC_TX_DISABLE_CHANNEL_SWITCH=y any channel with all these
    capabilities is marked DMA_ASYNC_TX allowing async_tx_find_channel() to
    quickly locate compatible channels with the guarantee that dependency
    chains will remain on one channel.  When
    ASYNC_TX_DISABLE_CHANNEL_SWITCH=n async_tx_find_channel() may select
    channels that lead to operation chains that need to cross channel
    boundaries using the async_tx channel switch capability.
    Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
    138f4c35
async_tx.c 7.8 KB