[PATCH] serial: Use -EAGAIN in getc and putc

["Pali Rohár" <pali@kernel.org>]

U-Boot serial code already handles -EAGAIN value from getc and putc
callbacks. So change drivers code to return -EAGAIN when HW is busy instead
of doing its own busy loop and waiting until HW is ready.

Signed-off-by: Pali Rohár <pali@kernel.org>
---
 drivers/serial/serial_arc.c         | 8 ++++----
 drivers/serial/serial_lpuart.c      | 8 ++++----
 drivers/serial/serial_mvebu_a3700.c | 8 ++++----
 3 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/serial/serial_arc.c b/drivers/serial/serial_arc.c
index b2d95bdbe18d..c2fc8a901e25 100644
--- a/drivers/serial/serial_arc.c
+++ b/drivers/serial/serial_arc.c
@@ -53,8 +53,8 @@ static int arc_serial_putc(struct udevice *dev, const char c)
 	struct arc_serial_plat *plat = dev_get_plat(dev);
 	struct arc_serial_regs *const regs = plat->reg;
 
-	while (!(readb(&regs->status) & UART_TXEMPTY))
-		;
+	if (!(readb(&regs->status) & UART_TXEMPTY))
+		return -EAGAIN;
 
 	writeb(c, &regs->data);
 
@@ -83,8 +83,8 @@ static int arc_serial_getc(struct udevice *dev)
 	struct arc_serial_plat *plat = dev_get_plat(dev);
 	struct arc_serial_regs *const regs = plat->reg;
 
-	while (!arc_serial_tstc(regs))
-		;
+	if (!arc_serial_tstc(regs))
+		return -EAGAIN;
 
 	/* Check for overflow errors */
 	if (readb(&regs->status) & UART_OVERFLOW_ERR)
diff --git a/drivers/serial/serial_lpuart.c b/drivers/serial/serial_lpuart.c
index ff576da516d4..d7259d531b55 100644
--- a/drivers/serial/serial_lpuart.c
+++ b/drivers/serial/serial_lpuart.c
@@ -168,8 +168,8 @@ static void _lpuart_serial_setbrg(struct udevice *dev,
 static int _lpuart_serial_getc(struct lpuart_serial_plat *plat)
 {
 	struct lpuart_fsl *base = plat->reg;
-	while (!(__raw_readb(&base->us1) & (US1_RDRF | US1_OR)))
-		schedule();
+	if (!(__raw_readb(&base->us1) & (US1_RDRF | US1_OR)))
+		return -EAGAIN;
 
 	barrier();
 
@@ -181,8 +181,8 @@ static void _lpuart_serial_putc(struct lpuart_serial_plat *plat,
 {
 	struct lpuart_fsl *base = plat->reg;
 
-	while (!(__raw_readb(&base->us1) & US1_TDRE))
-		schedule();
+	if (!(__raw_readb(&base->us1) & US1_TDRE))
+		return -EAGAIN;
 
 	__raw_writeb(c, &base->ud);
 }
diff --git a/drivers/serial/serial_mvebu_a3700.c b/drivers/serial/serial_mvebu_a3700.c
index 0fcd7e88acee..b2017c645565 100644
--- a/drivers/serial/serial_mvebu_a3700.c
+++ b/drivers/serial/serial_mvebu_a3700.c
@@ -40,8 +40,8 @@ static int mvebu_serial_putc(struct udevice *dev, const char ch)
 	struct mvebu_plat *plat = dev_get_plat(dev);
 	void __iomem *base = plat->base;
 
-	while (readl(base + UART_STATUS_REG) & UART_STATUS_TXFIFO_FULL)
-		;
+	if (readl(base + UART_STATUS_REG) & UART_STATUS_TXFIFO_FULL)
+		return -EAGAIN;
 
 	writel(ch, base + UART_TX_REG);
 
@@ -53,8 +53,8 @@ static int mvebu_serial_getc(struct udevice *dev)
 	struct mvebu_plat *plat = dev_get_plat(dev);
 	void __iomem *base = plat->base;
 
-	while (!(readl(base + UART_STATUS_REG) & UART_STATUS_RX_RDY))
-		;
+	if (!(readl(base + UART_STATUS_REG) & UART_STATUS_RX_RDY))
+		return -EAGAIN;
 
 	return readl(base + UART_RX_REG) & 0xff;
 }
-- 
2.20.1