[PATCH v2] 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>

---
Changes in v2:
* Fix serial_lpuart.c code after Tom's review
* Add serial_mpc8xx.c change

To prevent merge conflicts, please apply this patch *after* this:
http://patchwork.ozlabs.org/project/uboot/patch/20221210232744.15600-1-pali@kernel.org/
---
 drivers/serial/serial_arc.c         |  8 +++----
 drivers/serial/serial_lpuart.c      | 36 ++++++++++++-----------------
 drivers/serial/serial_mpc8xx.c      | 12 ++++------
 drivers/serial/serial_mvebu_a3700.c |  8 +++----
 4 files changed, 28 insertions(+), 36 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 07941c29ed74..51e66abdbc15 100644
--- a/drivers/serial/serial_lpuart.c
+++ b/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)))
-		schedule();
+	if (!(__raw_readb(&base->us1) & (US1_RDRF | US1_OR)))
+		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))
-		schedule();
+	if (!(__raw_readb(&base->us1) & US1_TDRE))
+		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();
-		lpuart_read32(plat->flags, &base->stat, &stat);
+		return -EAGAIN;
 	}
 
 	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);
-
-		if ((stat & STAT_TDRE))
-			break;
-
-		schedule();
-	}
+	lpuart_read32(plat->flags, &base->stat, &stat);
+	if (!(stat & STAT_TDRE))
+		return -EAGAIN;
 
 	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);
-	else
-		_lpuart_serial_putc(plat, c);
+		return _lpuart32_serial_putc(plat, c);
 
-	return 0;
+	return _lpuart_serial_putc(plat, c);
 }
 
 static int lpuart_serial_pending(struct udevice *dev, bool input)
diff --git a/drivers/serial/serial_mpc8xx.c b/drivers/serial/serial_mpc8xx.c
index 808a40f503ea..b8d6a81b650f 100644
--- a/drivers/serial/serial_mpc8xx.c
+++ b/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. */
-	while (in_be16(&rtx->rxbd.cbd_sc) & BD_SC_EMPTY)
-		schedule();
+	if (in_be16(&rtx->rxbd.cbd_sc) & BD_SC_EMPTY)
+		return -EAGAIN;
 
 	/* the characters are read one by one,
 	 * use the rxindex to know the next char to deliver
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