Certain users can not use right now the DMAengine API due to missing
features in the core. Prime example is Networking.

These users can use the glue layer interface to avoid misuse of DMAengine
API and when the core gains the needed features they can be converted to
use generic API.

The most prominent features the glue layer clients are depending on:

- most PSI-L native peripheral use extra rflow ranges on a receive channel
   and depending on the peripheral's configuration packets from a single
   free descriptor ring is going to be received to different receive ring
  - it is also possible to have different free descriptor rings per rflow
    and an rflow can also support 4 additional free descriptor ring based
    on the size of the incoming packet
- out of order completion of descriptors on a channel
 - when we have several queues to handle different priority packets the
   descriptors will be completed 'out-of-order'
- the notion of prep_slave_sg is not matching with what the streaming type
   of operation is demanding for networking
- Streaming type of operation
 - Ability to fill the free descriptor ring with descriptors in
   anticipation of incoming traffic and when a packet arrives UDMAP will
   form a packet and gives it to the client driver
 - the descriptors are not backed with exact size data buffers as we don't
   know the size of the packet we will receive, but as a generic pool of
   buffers to be used by the receive channel
- NAPI type of operation (polling instead of interrupt driven transfer)
 - without this we can not sustain gigabit speeds and we need to support NAPI
 - not to limit this to networking, but other high performance operations
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Keerthy <j-keerthy@ti.com>
Link: https://lore.kernel.org/r/20191223110458.30766-12-peter.ujfalusi@ti.comSigned-off-by: Vinod Koul <vkoul@kernel.org>