bcm283x_pl011: Flush RX queue after setting baud rate

After the UART was initialized, we may still have bogus data in the
RX queue if it was enabled with incorrect pin muxing before.

So let's flush the RX queue whenever we initialize baud rates.

This fixes a regression with the dynamic pinmuxing code when enable_uart=1
is not set in config.txt on Raspberry Pis that use pl011 for serial.

Fixes: caf2233b28 ("bcm283x: Add pinctrl driver")
Reported-by: Göran Lundberg <goran@lundberg.email>
Reported-by: Peter Robinson <pbrobinson@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Tested-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Tuomas Tynkkynen <tuomas@tuxera.com>

drivers/serial/serial_bcm283x_pl011.c

@@ -9,6 +9,7 @@
 #include <asm/gpio.h>
 #include <dm/pinctrl.h>
 #include <dm/platform_data/serial_pl01x.h>
+#include <serial.h>
 #include "serial_pl01x_internal.h"
 
 /*
@@ -55,6 +56,28 @@ static int bcm283x_pl011_serial_ofdata_to_platdata(struct udevice *dev)
 	return 0;
 }
 
+static int bcm283x_pl011_serial_setbrg(struct udevice *dev, int baudrate)
+{
+	int r;
+
+	r = pl01x_serial_setbrg(dev, baudrate);
+
+	/*
+	 * We may have been muxed to a bogus line before. Drain the RX
+	 * queue so we start at a clean slate.
+	 */
+	while (pl01x_serial_getc(dev) != -EAGAIN) ;
+
+	return r;
+}
+
+static const struct dm_serial_ops bcm283x_pl011_serial_ops = {
+	.putc = pl01x_serial_putc,
+	.pending = pl01x_serial_pending,
+	.getc = pl01x_serial_getc,
+	.setbrg = bcm283x_pl011_serial_setbrg,
+};
+
 static const struct udevice_id bcm283x_pl011_serial_id[] = {
 	{.compatible = "brcm,bcm2835-pl011", .data = TYPE_PL011},
 	{}
@@ -67,7 +90,7 @@ U_BOOT_DRIVER(bcm283x_pl011_uart) = {
 	.ofdata_to_platdata = of_match_ptr(bcm283x_pl011_serial_ofdata_to_platdata),
 	.platdata_auto_alloc_size = sizeof(struct pl01x_serial_platdata),
 	.probe	= pl01x_serial_probe,
-	.ops	= &pl01x_serial_ops,
+	.ops	= &bcm283x_pl011_serial_ops,
 	.flags	= DM_FLAG_PRE_RELOC,
 	.priv_auto_alloc_size = sizeof(struct pl01x_priv),
 };

drivers/serial/serial_pl01x.c

@@ -273,7 +273,7 @@ __weak struct serial_device *default_serial_console(void)
 
 #ifdef CONFIG_DM_SERIAL
 
-static int pl01x_serial_setbrg(struct udevice *dev, int baudrate)
+int pl01x_serial_setbrg(struct udevice *dev, int baudrate)
 {
 	struct pl01x_serial_platdata *plat = dev_get_platdata(dev);
 	struct pl01x_priv *priv = dev_get_priv(dev);
@@ -299,21 +299,21 @@ int pl01x_serial_probe(struct udevice *dev)
 		return 0;
 }
 
-static int pl01x_serial_getc(struct udevice *dev)
+int pl01x_serial_getc(struct udevice *dev)
 {
 	struct pl01x_priv *priv = dev_get_priv(dev);
 
 	return pl01x_getc(priv->regs);
 }
 
-static int pl01x_serial_putc(struct udevice *dev, const char ch)
+int pl01x_serial_putc(struct udevice *dev, const char ch)
 {
 	struct pl01x_priv *priv = dev_get_priv(dev);
 
 	return pl01x_putc(priv->regs, ch);
 }
 
-static int pl01x_serial_pending(struct udevice *dev, bool input)
+int pl01x_serial_pending(struct udevice *dev, bool input)
 {
 	struct pl01x_priv *priv = dev_get_priv(dev);
 	unsigned int fr = readl(&priv->regs->fr);
@@ -324,7 +324,7 @@ static int pl01x_serial_pending(struct udevice *dev, bool input)
 		return fr & UART_PL01x_FR_TXFF ? 0 : 1;
 }
 
-const struct dm_serial_ops pl01x_serial_ops = {
+static const struct dm_serial_ops pl01x_serial_ops = {
 	.putc = pl01x_serial_putc,
 	.pending = pl01x_serial_pending,
 	.getc = pl01x_serial_getc,

drivers/serial/serial_pl01x_internal.h

@@ -43,7 +43,12 @@ struct pl01x_regs {
 
 int pl01x_serial_ofdata_to_platdata(struct udevice *dev);
 int pl01x_serial_probe(struct udevice *dev);
-extern const struct dm_serial_ops pl01x_serial_ops;
+
+/* Needed for external pl01x_serial_ops drivers */
+int pl01x_serial_putc(struct udevice *dev, const char ch);
+int pl01x_serial_pending(struct udevice *dev, bool input);
+int pl01x_serial_getc(struct udevice *dev);
+int pl01x_serial_setbrg(struct udevice *dev, int baudrate);
 
 struct pl01x_priv {
 	struct pl01x_regs *regs;