tty: serial: fsl_lpuart: implement module parameter to disable DMA

The DMA implementation has been and is still affected by bugs and
race conditions. To bridge the time until those have been addressed,
add fsl-lpuart.nodma module parameter which allows to disable the
UART DMA using a kernel argument.

1 files changed, 16 insertions, 9 deletions

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 1f52532ce943..f6549ac5a8cf 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -230,6 +230,9 @@
 #define DEV_NAME	"ttyLP"
 #define UART_NR		6
 
+static bool nodma = true;
+module_param(nodma, bool, S_IRUGO);
+
 struct lpuart_port {
 	struct uart_port	port;
 	struct clk		*clk;
@@ -1795,6 +1798,15 @@ static struct uart_driver lpuart_reg = {
 	.cons		= LPUART_CONSOLE,
 };
 
+static void lpuart_request_dma_chan(struct lpuart_port *sport,
+				    struct dma_chan *chan, const char *name)
+{
+	chan = dma_request_slave_channel(sport->port.dev, name);
+	if (!chan)
+		dev_info(sport->port.dev, "DMA %s channel request failed, "
+				"operating without %s DMA\n", name, name);
+}
+
 static int lpuart_probe(struct platform_device *pdev)
 {
 	struct device_node *np = pdev->dev.of_node;
@@ -1864,15 +1876,10 @@ static int lpuart_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	sport->dma_tx_chan = dma_request_slave_channel(sport->port.dev, "tx");
-	if (!sport->dma_tx_chan)
-		dev_info(sport->port.dev, "DMA tx channel request failed, "
-				"operating without tx DMA\n");
-
-	sport->dma_rx_chan = dma_request_slave_channel(sport->port.dev, "rx");
-	if (!sport->dma_rx_chan)
-		dev_info(sport->port.dev, "DMA rx channel request failed, "
-				"operating without rx DMA\n");
+	if (!nodma) {
+		lpuart_request_dma_chan(sport, sport->dma_tx_chan, "tx");
+		lpuart_request_dma_chan(sport, sport->dma_rx_chan, "rx");
+	}
 
 	if (of_property_read_bool(np, "linux,rs485-enabled-at-boot-time")) {
 		sport->port.rs485.flags |= SER_RS485_ENABLED;