serial: 8250: Validate dmaengine tx chan meets requirements

8250 dma support requires the dmaegine driver support terminate.
Query slave caps to determine if necessary commands/properties are
supported; disable dma if not.

Note this means dmaengine driver must support slave caps reporting
as well.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_dma.c

@@ -201,6 +201,15 @@ int serial8250_request_dma(struct uart_8250_port *p)
 		goto release_rx;
 	}
 
+	/* 8250 tx dma requires dmaengine driver to support terminate */
+	ret = dma_get_slave_caps(dma->txchan, &caps);
+	if (ret)
+		goto err;
+	if (!caps.cmd_terminate) {
+		ret = -EINVAL;
+		goto err;
+	}
+
 	dmaengine_slave_config(dma->txchan, &dma->txconf);
 
 	/* RX buffer */