commit 8836384c754295b1bbbb2910664c0d07de0dbde4
author Sagar Shrikant Kadam <sagar.kadam@sifive.com> Tue Jul 09 05:23:44 2019 -0700
committer Andes <uboot@andestech.com> Thu Aug 15 13:42:28 2019 +0800
tree b648be5a4a39ff52d4573120d385a4f439091a3c
parent df33f8646855e65b8e7232c7fd5739e1ae1eb58b

riscv : serial: use rx watermark to indicate rx data is present

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@sifive.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>
Tested-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Padmarao Begari <padmarao.begari@microchip.com>
Tested-by: Padmarao Begari <padmarao.begari@microchip.com>

drivers/serial/serial_sifive.c

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 @@
 #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 sifive_uart_platdata {
 	unsigned long clock;
-	int saved_input_char;
 	struct uart_sifive *regs;
 };
 
@@ -94,7 +96,7 @@
 		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 @@
 	if (gd->flags & GD_FLG_RELOC)
 		return 0;
 
-	platdata->saved_input_char = 0;
 	_sifive_serial_init(platdata->regs);
 
 	return 0;
@@ -145,12 +146,6 @@
 	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 @@
 	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)