[PATCH 2/7] serial: stm32: fix rx error handling

[Erwan Le Ray <erwan.leray@st.com>]

- Fixes parity and framing error bit by clearing parity and framing error
  flag. The current implementation doesn't clear the error bits when an
  error is detected.
- Fixes the incorrect name of framing error clearing flag in header file.
- Fixes misalignement between data frame and errors status. The status
  read for "n" frame was the status of "n+1" frame".
- Fixes break detection was not triggered by the expected register.

Fixes: 48a6092fb41f ("serial: stm32-usart: Add STM32 USART Driver")
Signed-off-by: Erwan Le Ray <erwan.leray@st.com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index e832185..f6b7393 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -225,35 +225,51 @@ static void stm32_receive_chars(struct uart_port *port, bool threaded)
 
 	while (stm32_pending_rx(port, &sr, &stm32_port->last_res, threaded)) {
 		sr |= USART_SR_DUMMY_RX;
-		c = stm32_get_char(port, &sr, &stm32_port->last_res);
 		flag = TTY_NORMAL;
-		port->icount.rx++;
 
+		/*
+		 * Status bits has to be cleared before reading the RDR:
+		 * In FIFO mode, reading the RDR will pop the next data
+		 * (if any) along with its status bits into the SR.
+		 * Not doing so leads to misalignement between RDR and SR,
+		 * and clear status bits of the next rx data.
+		 *
+		 * Clear errors flags for stm32f7 and stm32h7 compatible
+		 * devices. On stm32f4 compatible devices, the error bit is
+		 * cleared by the sequence [read SR - read DR].
+		 */
+		if ((sr & USART_SR_ERR_MASK) && ofs->icr != UNDEF_REG)
+			stm32_clr_bits(port, ofs->icr, USART_ICR_ORECF |
+				       USART_ICR_PECF | USART_ICR_FECF);
+
+		c = stm32_get_char(port, &sr, &stm32_port->last_res);
+		port->icount.rx++;
 		if (sr & USART_SR_ERR_MASK) {
-			if (sr & USART_SR_LBD) {
-				port->icount.brk++;
-				if (uart_handle_break(port))
-					continue;
-			} else if (sr & USART_SR_ORE) {
-				if (ofs->icr != UNDEF_REG)
-					writel_relaxed(USART_ICR_ORECF,
-						       port->membase +
-						       ofs->icr);
+			if (sr & USART_SR_ORE) {
 				port->icount.overrun++;
 			} else if (sr & USART_SR_PE) {
 				port->icount.parity++;
 			} else if (sr & USART_SR_FE) {
-				port->icount.frame++;
+				/* Break detection if character is null */
+				if (!c) {
+					port->icount.brk++;
+					if (uart_handle_break(port))
+						continue;
+				} else {
+					port->icount.frame++;
+				}
 			}
 
 			sr &= port->read_status_mask;
 
-			if (sr & USART_SR_LBD)
-				flag = TTY_BREAK;
-			else if (sr & USART_SR_PE)
+			if (sr & USART_SR_PE) {
 				flag = TTY_PARITY;
-			else if (sr & USART_SR_FE)
-				flag = TTY_FRAME;
+			} else if (sr & USART_SR_FE) {
+				if (!c)
+					flag = TTY_BREAK;
+				else
+					flag = TTY_FRAME;
+			}
 		}
 
 		if (uart_handle_sysrq_char(port, c))
@@ -721,14 +737,14 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
 	if (termios->c_iflag & INPCK)
 		port->read_status_mask |= USART_SR_PE | USART_SR_FE;
 	if (termios->c_iflag & (IGNBRK | BRKINT | PARMRK))
-		port->read_status_mask |= USART_SR_LBD;
+		port->read_status_mask |= USART_SR_FE;
 
 	/* Characters to ignore */
 	port->ignore_status_mask = 0;
 	if (termios->c_iflag & IGNPAR)
 		port->ignore_status_mask = USART_SR_PE | USART_SR_FE;
 	if (termios->c_iflag & IGNBRK) {
-		port->ignore_status_mask |= USART_SR_LBD;
+		port->ignore_status_mask |= USART_SR_FE;
 		/*
 		 * If we're ignoring parity and break indicators,
 		 * ignore overruns too (for real raw support).
diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index a70aa50..8d34802 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -108,7 +108,6 @@ struct stm32_usart_info stm32h7_info = {
 #define USART_SR_RXNE		BIT(5)
 #define USART_SR_TC		BIT(6)
 #define USART_SR_TXE		BIT(7)
-#define USART_SR_LBD		BIT(8)
 #define USART_SR_CTSIF		BIT(9)
 #define USART_SR_CTS		BIT(10)		/* F7 */
 #define USART_SR_RTOF		BIT(11)		/* F7 */
@@ -120,8 +119,7 @@ struct stm32_usart_info stm32h7_info = {
 #define USART_SR_SBKF		BIT(18)		/* F7 */
 #define USART_SR_WUF		BIT(20)		/* H7 */
 #define USART_SR_TEACK		BIT(21)		/* F7 */
-#define USART_SR_ERR_MASK	(USART_SR_LBD | USART_SR_ORE | \
-				 USART_SR_FE | USART_SR_PE)
+#define USART_SR_ERR_MASK	(USART_SR_ORE | USART_SR_FE | USART_SR_PE)
 /* Dummy bits */
 #define USART_SR_DUMMY_RX	BIT(16)
 
@@ -168,8 +166,6 @@ struct stm32_usart_info stm32h7_info = {
 /* USART_CR2 */
 #define USART_CR2_ADD_MASK	GENMASK(3, 0)	/* F4 */
 #define USART_CR2_ADDM7		BIT(4)		/* F7 */
-#define USART_CR2_LBDL		BIT(5)
-#define USART_CR2_LBDIE		BIT(6)
 #define USART_CR2_LBCL		BIT(8)
 #define USART_CR2_CPHA		BIT(9)
 #define USART_CR2_CPOL		BIT(10)
@@ -226,12 +222,10 @@ struct stm32_usart_info stm32h7_info = {
 
 /* USART_ICR */
 #define USART_ICR_PECF		BIT(0)		/* F7 */
-#define USART_ICR_FFECF		BIT(1)		/* F7 */
-#define USART_ICR_NCF		BIT(2)		/* F7 */
+#define USART_ICR_FECF		BIT(1)		/* F7 */
 #define USART_ICR_ORECF		BIT(3)		/* F7 */
 #define USART_ICR_IDLECF	BIT(4)		/* F7 */
 #define USART_ICR_TCCF		BIT(6)		/* F7 */
-#define USART_ICR_LBDCF		BIT(8)		/* F7 */
 #define USART_ICR_CTSCF		BIT(9)		/* F7 */
 #define USART_ICR_RTOCF		BIT(11)		/* F7 */
 #define USART_ICR_EOBCF		BIT(12)		/* F7 */
-- 
1.9.1


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