serial: Use -EAGAIN in getc and putc

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

@@ -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)

drivers/serial/serial_lpuart.c

@@ -168,23 +168,24 @@ 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)))
+	if (!(__raw_readb(&base->us1) & (US1_RDRF | US1_OR)))
-		schedule();
+		return -EAGAIN;
 
 	barrier();
 
 	return __raw_readb(&base->ud);
 }
 
-static void _lpuart_serial_putc(struct lpuart_serial_plat *plat,
+static int _lpuart_serial_putc(struct lpuart_serial_plat *plat,
 				const char c)
 {
 	struct lpuart_fsl *base = plat->reg;
 
-	while (!(__raw_readb(&base->us1) & US1_TDRE))
+	if (!(__raw_readb(&base->us1) & US1_TDRE))
-		schedule();
+		return -EAGAIN;
 
 	__raw_writeb(c, &base->ud);
+	return 0;
 }
 
 /* Test whether a character is in the RX buffer */
@@ -328,10 +329,9 @@ static int _lpuart32_serial_getc(struct lpuart_serial_plat *plat)
 	u32 stat, val;
 
 	lpuart_read32(plat->flags, &base->stat, &stat);
-	while ((stat & STAT_RDRF) == 0) {
+	if ((stat & STAT_RDRF) == 0) {
 		lpuart_write32(plat->flags, &base->stat, STAT_FLAGS);
-		schedule();
+		return -EAGAIN;
-		lpuart_read32(plat->flags, &base->stat, &stat);
 	}
 
 	lpuart_read32(plat->flags, &base->data, &val);
@@ -343,22 +343,18 @@ static int _lpuart32_serial_getc(struct lpuart_serial_plat *plat)
 	return val & 0x3ff;
 }
 
-static void _lpuart32_serial_putc(struct lpuart_serial_plat *plat,
+static int _lpuart32_serial_putc(struct lpuart_serial_plat *plat,
 				  const char c)
 {
 	struct lpuart_fsl_reg32 *base = plat->reg;
 	u32 stat;
 
-	while (true) {
+	lpuart_read32(plat->flags, &base->stat, &stat);
-		lpuart_read32(plat->flags, &base->stat, &stat);
+	if (!(stat & STAT_TDRE))
-
+		return -EAGAIN;
-		if ((stat & STAT_TDRE))
-			break;
-
-		schedule();
-	}
 
 	lpuart_write32(plat->flags, &base->data, c);
+	return 0;
 }
 
 /* Test whether a character is in the RX buffer */
@@ -453,11 +449,9 @@ static int lpuart_serial_putc(struct udevice *dev, const char c)
 	struct lpuart_serial_plat *plat = dev_get_plat(dev);
 
 	if (is_lpuart32(dev))
-		_lpuart32_serial_putc(plat, c);
+		return _lpuart32_serial_putc(plat, c);
-	else
-		_lpuart_serial_putc(plat, c);
 
-	return 0;
+	return _lpuart_serial_putc(plat, c);
 }
 
 static int lpuart_serial_pending(struct udevice *dev, bool input)

drivers/serial/serial_mpc8xx.c

@@ -178,14 +178,13 @@ static int serial_mpc8xx_putc(struct udevice *dev, const char c)
 
 	rtx = (struct serialbuffer __iomem *)&cpmp->cp_dpmem[CPM_SERIAL_BASE];
 
-	/* Wait for last character to go. */
+	if (in_be16(&rtx->txbd.cbd_sc) & BD_SC_READY)
+		return -EAGAIN;
+
 	out_8(&rtx->txbuf, c);
 	out_be16(&rtx->txbd.cbd_datlen, 1);
 	setbits_be16(&rtx->txbd.cbd_sc, BD_SC_READY);
 
-	while (in_be16(&rtx->txbd.cbd_sc) & BD_SC_READY)
-		schedule();
-
 	return 0;
 }
 
@@ -199,9 +198,8 @@ static int serial_mpc8xx_getc(struct udevice *dev)
 
 	rtx = (struct serialbuffer __iomem *)&cpmp->cp_dpmem[CPM_SERIAL_BASE];
 
-	/* Wait for character to show up. */
+	if (in_be16(&rtx->rxbd.cbd_sc) & BD_SC_EMPTY)
-	while (in_be16(&rtx->rxbd.cbd_sc) & BD_SC_EMPTY)
+		return -EAGAIN;
-		schedule();
 
 	/* the characters are read one by one,
 	 * use the rxindex to know the next char to deliver

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;
 }