[U-Boot] [PATCH] riscv : serial: use rx watermark to indicate rx data is present

[Sagar Shrikant Kadam]

In y-modem transfer mode, tstc/getc fail to check if there is any
data available / received in RX FIFO, and so y-modem transfer never
succeeds. Using receive watermark bit within ip register fixes the
issue.

This patch is based on commit c7392b7bc4e1 ("Use the RX watermark
interrupt pending bit for TSTC") available at[1]

[1] https://github.com/sifive/HiFive_U-Boot/tree/regression

Signed-off-by: Sagar Shrikant Kadam <sagar.kadam at sifive.com>
---

 drivers/serial/serial_sifive.c | 23 +++++++----------------
 1 file changed, 7 insertions(+), 16 deletions(-)

diff --git a/drivers/serial/serial_sifive.c b/drivers/serial/serial_sifive.c
index fdfef69..c142ccd 100644
--- a/drivers/serial/serial_sifive.c
+++ b/drivers/serial/serial_sifive.c
@@ -22,6 +22,9 @@ DECLARE_GLOBAL_DATA_PTR;
 #define UART_TXCTRL_TXEN	0x1
 #define UART_RXCTRL_RXEN	0x1
 
+/* IP register */
+#define UART_IP_RXWM            0x2
+
 struct uart_sifive {
 	u32 txfifo;
 	u32 rxfifo;
@@ -34,7 +37,6 @@ struct uart_sifive {
 
 struct sifive_uart_platdata {
 	unsigned long clock;
-	int saved_input_char;
 	struct uart_sifive *regs;
 };
 
@@ -94,7 +96,7 @@ static int _sifive_serial_getc(struct uart_sifive *regs)
 		return -EAGAIN;
 	ch &= UART_RXFIFO_DATA;
 
-	return (!ch) ? -EAGAIN : ch;
+	return ch;
 }
 
 static int sifive_serial_setbrg(struct udevice *dev, int baudrate)
@@ -133,7 +135,6 @@ static int sifive_serial_probe(struct udevice *dev)
 	if (gd->flags & GD_FLG_RELOC)
 		return 0;
 
-	platdata->saved_input_char = 0;
 	_sifive_serial_init(platdata->regs);
 
 	return 0;
@@ -145,12 +146,6 @@ static int sifive_serial_getc(struct udevice *dev)
 	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
 	struct uart_sifive *regs = platdata->regs;
 
-	if (platdata->saved_input_char > 0) {
-		c = platdata->saved_input_char;
-		platdata->saved_input_char = 0;
-		return c;
-	}
-
 	while ((c = _sifive_serial_getc(regs)) == -EAGAIN) ;
 
 	return c;
@@ -171,14 +166,10 @@ static int sifive_serial_pending(struct udevice *dev, bool input)
 	struct sifive_uart_platdata *platdata = dev_get_platdata(dev);
 	struct uart_sifive *regs = platdata->regs;
 
-	if (input) {
-		if (platdata->saved_input_char > 0)
-			return 1;
-		platdata->saved_input_char = _sifive_serial_getc(regs);
-		return (platdata->saved_input_char > 0) ? 1 : 0;
-	} else {
+	if (input)
+		return (readl(&regs->ip) & UART_IP_RXWM);
+	else
 		return !!(readl(&regs->txfifo) & UART_TXFIFO_FULL);
-	}
 }
 
 static int sifive_serial_ofdata_to_platdata(struct udevice *dev)
-- 
2.7.4