serial: serial-uclass: Add generic serial RX buffer support

Pasting longer lines into the U-Boot console prompt sometimes leads to
characters missing. One problem here is the small 16-byte FIFO of the
legacy NS16550 UART, e.g. on x86 platforms.

This patch now introduces a Kconfig option to enable RX buffer support
for all DM based serial drivers. With this option enabled, I was
able paste really long lines into the U-Boot console, without any
characters missing.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Tom Rini <trini@konsulko.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

drivers/serial/Kconfig

@@ -64,6 +64,21 @@ config DM_SERIAL
 	  implements serial_putc() etc. The uclass interface is
 	  defined in include/serial.h.
 
+config SERIAL_RX_BUFFER
+	bool "Enable RX buffer for serial input"
+	depends on DM_SERIAL
+	help
+	  Enable RX buffer support for the serial driver. This enables
+	  pasting longer strings, even when the RX FIFO of the UART is
+	  not big enough (e.g. 16 bytes on the normal NS16550).
+
+config SERIAL_RX_BUFFER_SIZE
+	int "RX buffer size"
+	depends on SERIAL_RX_BUFFER
+	default 256
+	help
+	  The size of the RX buffer (needs to be power of 2)
+
 config SPL_DM_SERIAL
 	bool "Enable Driver Model for serial drivers in SPL"
 	depends on DM_SERIAL

drivers/serial/serial-uclass.c

@@ -160,7 +160,7 @@ static void _serial_puts(struct udevice *dev, const char *str)
 		_serial_putc(dev, *str++);
 }
 
-static int _serial_getc(struct udevice *dev)
+static int __serial_getc(struct udevice *dev)
 {
 	struct dm_serial_ops *ops = serial_get_ops(dev);
 	int err;
@@ -174,7 +174,7 @@ static int _serial_getc(struct udevice *dev)
 	return err >= 0 ? err : 0;
 }
 
-static int _serial_tstc(struct udevice *dev)
+static int __serial_tstc(struct udevice *dev)
 {
 	struct dm_serial_ops *ops = serial_get_ops(dev);
 
@@ -184,6 +184,44 @@ static int _serial_tstc(struct udevice *dev)
 	return 1;
 }
 
+#if CONFIG_IS_ENABLED(SERIAL_RX_BUFFER)
+static int _serial_tstc(struct udevice *dev)
+{
+	struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
+
+	/* Read all available chars into the RX buffer */
+	while (__serial_tstc(dev)) {
+		upriv->buf[upriv->wr_ptr++] = __serial_getc(dev);
+		upriv->wr_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
+	}
+
+	return upriv->rd_ptr != upriv->wr_ptr ? 1 : 0;
+}
+
+static int _serial_getc(struct udevice *dev)
+{
+	struct serial_dev_priv *upriv = dev_get_uclass_priv(dev);
+	char val;
+
+	val = upriv->buf[upriv->rd_ptr++];
+	upriv->rd_ptr %= CONFIG_SERIAL_RX_BUFFER_SIZE;
+
+	return val;
+}
+
+#else /* CONFIG_IS_ENABLED(SERIAL_RX_BUFFER) */
+
+static int _serial_getc(struct udevice *dev)
+{
+	return __serial_getc(dev);
+}
+
+static int _serial_tstc(struct udevice *dev)
+{
+	return __serial_tstc(dev);
+}
+#endif /* CONFIG_IS_ENABLED(SERIAL_RX_BUFFER) */
+
 void serial_putc(char ch)
 {
 	if (gd->cur_serial_dev)
@@ -359,6 +397,12 @@ static int serial_post_probe(struct udevice *dev)
 	sdev.puts = serial_stub_puts;
 	sdev.getc = serial_stub_getc;
 	sdev.tstc = serial_stub_tstc;
+
+#if CONFIG_IS_ENABLED(SERIAL_RX_BUFFER)
+	/* Allocate the RX buffer */
+	upriv->buf = malloc(CONFIG_SERIAL_RX_BUFFER_SIZE);
+#endif
+
 	stdio_register_dev(&sdev, &upriv->sdev);
 #endif
 	return 0;

include/serial.h

@@ -148,10 +148,18 @@ struct dm_serial_ops {
 /**
  * struct serial_dev_priv - information about a device used by the uclass
  *
- * @sdev: stdio device attached to this uart
+ * @sdev:	stdio device attached to this uart
+ *
+ * @buf:	Pointer to the RX buffer
+ * @rd_ptr:	Read pointer in the RX buffer
+ * @wr_ptr:	Write pointer in the RX buffer
  */
 struct serial_dev_priv {
 	struct stdio_dev *sdev;
+
+	char *buf;
+	int rd_ptr;
+	int wr_ptr;
 };
 
 /* Access the serial operations for a device */