serial: serial_stm32: Enable overrun

Enable uart overrun feature which allows to benefits of uart
FIFO usage.

Previously overrun management was disabled, this has to effect
to bypassed the uart FIFO usage even if FIFO was enabled.
In particular configuration, for example when video console is
enabled, copy/pasting a long command line in console results in
corruption. This is due to the fact that a lot of time is consumed
in flushing the cache during frame buffer update, so uart chars are
not read fast enough.

By using uart FIFO and managing overrun, long command line can by
copy/paste in console without being corrupted.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

drivers/serial/serial_stm32.c

@@ -43,10 +43,19 @@ static int stm32_serial_getc(struct udevice *dev)
 	struct stm32x7_serial_platdata *plat = dev_get_platdata(dev);
 	bool stm32f4 = plat->uart_info->stm32f4;
 	fdt_addr_t base = plat->base;
+	u32 isr = readl(base + ISR_OFFSET(stm32f4));
 
-	if ((readl(base + ISR_OFFSET(stm32f4)) & USART_SR_FLAG_RXNE) == 0)
+	if ((isr & USART_SR_FLAG_RXNE) == 0)
 		return -EAGAIN;
 
+	if (isr & USART_SR_FLAG_ORE) {
+		if (!stm32f4)
+			setbits_le32(base + ICR_OFFSET, USART_ICR_OREF);
+		else
+			readl(base + RDR_OFFSET(stm32f4));
+		return -EIO;
+	}
+
 	return readl(base + RDR_OFFSET(stm32f4));
 }
 
@@ -107,11 +116,9 @@ static int stm32_serial_probe(struct udevice *dev)
 		return plat->clock_rate;
 	};
 
-	/* Disable uart-> disable overrun-> enable uart */
+	/* Disable uart-> enable fifo-> enable uart */
 	clrbits_le32(base + CR1_OFFSET(stm32f4), USART_CR1_RE | USART_CR1_TE |
 		     BIT(uart_enable_bit));
-	if (plat->uart_info->has_overrun_disable)
-		setbits_le32(base + CR3_OFFSET(stm32f4), USART_CR3_OVRDIS);
 	if (plat->uart_info->has_fifo)
 		setbits_le32(base + CR1_OFFSET(stm32f4), USART_CR1_FIFOEN);
 	setbits_le32(base + CR1_OFFSET(stm32f4), USART_CR1_RE | USART_CR1_TE |

drivers/serial/serial_stm32.h

@@ -12,6 +12,8 @@
 #define CR3_OFFSET(x)	(x ? 0x14 : 0x08)
 #define BRR_OFFSET(x)	(x ? 0x08 : 0x0c)
 #define ISR_OFFSET(x)	(x ? 0x00 : 0x1c)
+
+#define ICR_OFFSET	0x20
 /*
  * STM32F4 has one Data Register (DR) for received or transmitted
  * data, so map Receive Data Register (RDR) and Transmit Data
@@ -23,28 +25,24 @@
 struct stm32_uart_info {
 	u8 uart_enable_bit;	/* UART_CR1_UE */
 	bool stm32f4;		/* true for STM32F4, false otherwise */
-	bool has_overrun_disable;
 	bool has_fifo;
 };
 
 struct stm32_uart_info stm32f4_info = {
 	.stm32f4 = true,
 	.uart_enable_bit = 13,
-	.has_overrun_disable = false,
 	.has_fifo = false,
 };
 
 struct stm32_uart_info stm32f7_info = {
 	.uart_enable_bit = 0,
 	.stm32f4 = false,
-	.has_overrun_disable = true,
 	.has_fifo = false,
 };
 
 struct stm32_uart_info stm32h7_info = {
 	.uart_enable_bit = 0,
 	.stm32f4 = false,
-	.has_overrun_disable = true,
 	.has_fifo = true,
 };
 
@@ -62,6 +60,7 @@ struct stm32x7_serial_platdata {
 
 #define USART_CR3_OVRDIS		BIT(12)
 
+#define USART_SR_FLAG_ORE		BIT(3)
 #define USART_SR_FLAG_RXNE		BIT(5)
 #define USART_SR_FLAG_TXE		BIT(7)
 
@@ -69,4 +68,5 @@ struct stm32x7_serial_platdata {
 #define USART_BRR_M_SHIFT		4
 #define USART_BRR_M_MASK		GENMASK(15, 4)
 
+#define USART_ICR_OREF			BIT(3)
 #endif