tty: serial: uartlite: Prevent changing fixed parameters

This device does not support changing baud, parity, data bits, stop
bits, or detecting breaks. Disable "changing" these settings to prevent
their termios from diverging from the actual state of the uart.

In order to determine the correct parameters to enforce, we read the
various new devicetree parameters to discover how the uart was
configured when it was synthesized. The defaults match
ulite_console_setup. xlnx,use-parity, xlnx,odd-parity, and
xlnx,data-bits are optional since there were in-tree users (and
presumably out-of-tree users) who did not set them.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20210826192154.3202269-5-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/uartlite.c

@@ -8,6 +8,7 @@
 
 #include <linux/platform_device.h>
 #include <linux/module.h>
+#include <linux/bitfield.h>
 #include <linux/console.h>
 #include <linux/serial.h>
 #include <linux/serial_core.h>
@@ -63,9 +64,18 @@
 static struct uart_port *console_port;
 #endif
 
+/**
+ * struct uartlite_data: Driver private data
+ * reg_ops: Functions to read/write registers
+ * clk: Our parent clock, if present
+ * baud: The baud rate configured when this device was synthesized
+ * cflags: The cflags for parity and data bits
+ */
 struct uartlite_data {
 	const struct uartlite_reg_ops *reg_ops;
 	struct clk *clk;
+	unsigned int baud;
+	tcflag_t cflags;
 };
 
 struct uartlite_reg_ops {
@@ -119,6 +129,8 @@ static inline void uart_out32(u32 val, u32 offset, struct uart_port *port)
 
 static struct uart_port ulite_ports[ULITE_NR_UARTS];
 
+static struct uart_driver ulite_uart_driver;
+
 /* ---------------------------------------------------------------------
  * Core UART driver operations
  */
@@ -306,7 +318,12 @@ static void ulite_set_termios(struct uart_port *port, struct ktermios *termios,
 			      struct ktermios *old)
 {
 	unsigned long flags;
-	unsigned int baud;
+	struct uartlite_data *pdata = port->private_data;
+
+	/* Set termios to what the hardware supports */
+	termios->c_cflag &= ~(BRKINT | CSTOPB | PARENB | PARODD | CSIZE);
+	termios->c_cflag |= pdata->cflags & (PARENB | PARODD | CSIZE);
+	tty_termios_encode_baud_rate(termios, pdata->baud, pdata->baud);
 
 	spin_lock_irqsave(&port->lock, flags);
 
@@ -329,8 +346,7 @@ static void ulite_set_termios(struct uart_port *port, struct ktermios *termios,
 			| ULITE_STATUS_FRAME | ULITE_STATUS_OVERRUN;
 
 	/* update timeout */
-	baud = uart_get_baud_rate(port, termios, old, 0, 460800);
-	uart_update_timeout(port, termios->c_cflag, baud);
+	uart_update_timeout(port, termios->c_cflag, pdata->baud);
 
 	spin_unlock_irqrestore(&port->lock, flags);
 }
@@ -532,8 +548,6 @@ static int ulite_console_setup(struct console *co, char *options)
 	return uart_set_options(port, co, baud, parity, bits, flow);
 }
 
-static struct uart_driver ulite_uart_driver;
-
 static struct console ulite_console = {
 	.name	= ULITE_NAME,
 	.write	= ulite_console_write,
@@ -765,18 +779,73 @@ static int ulite_probe(struct platform_device *pdev)
 	struct uartlite_data *pdata;
 	int irq, ret;
 	int id = pdev->id;
-#ifdef CONFIG_OF
-	const __be32 *prop;
 
-	prop = of_get_property(pdev->dev.of_node, "port-number", NULL);
-	if (prop)
-		id = be32_to_cpup(prop);
-#endif
 	pdata = devm_kzalloc(&pdev->dev, sizeof(struct uartlite_data),
 			     GFP_KERNEL);
 	if (!pdata)
 		return -ENOMEM;
 
+	if (IS_ENABLED(CONFIG_OF)) {
+		const char *prop;
+		struct device_node *np = pdev->dev.of_node;
+		u32 val = 0;
+
+		prop = "port-number";
+		ret = of_property_read_u32(np, prop, &id);
+		if (ret && ret != -EINVAL)
+of_err:
+			return dev_err_probe(&pdev->dev, ret,
+					     "could not read %s\n", prop);
+
+		prop = "current-speed";
+		ret = of_property_read_u32(np, prop, &pdata->baud);
+		if (ret)
+			goto of_err;
+
+		prop = "xlnx,use-parity";
+		ret = of_property_read_u32(np, prop, &val);
+		if (ret && ret != -EINVAL)
+			goto of_err;
+
+		if (val) {
+			prop = "xlnx,odd-parity";
+			ret = of_property_read_u32(np, prop, &val);
+			if (ret)
+				goto of_err;
+
+			if (val)
+				pdata->cflags |= PARODD;
+			pdata->cflags |= PARENB;
+		}
+
+		val = 8;
+		prop = "xlnx,data-bits";
+		ret = of_property_read_u32(np, prop, &val);
+		if (ret && ret != -EINVAL)
+			goto of_err;
+
+		switch (val) {
+		case 5:
+			pdata->cflags |= CS5;
+			break;
+		case 6:
+			pdata->cflags |= CS6;
+			break;
+		case 7:
+			pdata->cflags |= CS7;
+			break;
+		case 8:
+			pdata->cflags |= CS8;
+			break;
+		default:
+			return dev_err_probe(&pdev->dev, -EINVAL,
+					     "bad data bits %d\n", val);
+		}
+	} else {
+		pdata->baud = 9600;
+		pdata->cflags = CS8;
+	}
+
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	if (!res)
 		return -ENODEV;