linux-phytec-ti

serial: 8250: 8250_omap: Fix DMA teardown sequence during RX timeout

Calling dmaengine_terminate_async() does not guarantee all the data that
is picked up DMA and is in flight to memory is flushed immediately,
therefore poll for the in flight data to be flushed before pushing
buffer to tty ldisc.
Ideal way to solve this without polling is to call
dmaengine_synchronize() before pushing data to tty layer, but that
cannot be done in interrupt context and code cannot be moved to bottom
half as we need to hold rx_dma_lock spinlock.
Therefore introduce a bounded polling mechanism to know data has been
flushed. Since this is a flush at DMA hardware level, sequence should be
quite deterministic and loop upper bound is set to 5 times the observed
value.

Tested-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>