serial: tegra: Read DMA status before terminating

Read the DMA status before terminating the DMA, as doing so deletes
the DMA desc.

Also, to get the correct transfer status information, pause the DMA
using dmaengine_pause() before reading the DMA status.

Fixes: e9ea096dd225 ("serial: tegra: add serial driver")
Reviewed-by: Jon Hunter <[e-mail]>
Reviewed-by: Ilpo Järvinen <[e-mail]>
Acked-by: Thierry Reding <[e-mail]>
Signed-off-by: Akhil R <[e-mail]>
Signed-off-by: Kartik <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/serial-tegra.c

···
 	if (tup->tx_in_progress != TEGRA_UART_TX_DMA)
 		return;
 
-	dmaengine_terminate_all(tup->tx_dma_chan);
+	dmaengine_pause(tup->tx_dma_chan);
 	dmaengine_tx_status(tup->tx_dma_chan, tup->tx_cookie, &state);
+	dmaengine_terminate_all(tup->tx_dma_chan);
 	count = tup->tx_bytes_requested - state.residue;
 	async_tx_ack(tup->tx_dma_desc);
 	uart_xmit_advance(&tup->uport, count);
···
 		return;
 	}
 
-	dmaengine_terminate_all(tup->rx_dma_chan);
+	dmaengine_pause(tup->rx_dma_chan);
 	dmaengine_tx_status(tup->rx_dma_chan, tup->rx_cookie, &state);
+	dmaengine_terminate_all(tup->rx_dma_chan);
 
 	tegra_uart_rx_buffer_push(tup, state.residue);
 	tup->rx_dma_active = false;