linux-kernel - [PATCH 5/5] serial: stm32: add RX and TX FIFO flush

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Message-ID: <1560852146-3393-6-git-send-email-erwan.leray@st.com>
Date:   Tue, 18 Jun 2019 12:02:26 +0200
From:   Erwan Le Ray <erwan.leray@...com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        "Alexandre Torgue" <alexandre.torgue@...com>
CC:     <linux-serial@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "Erwan Le Ray" <erwan.leray@...com>,
        Fabrice Gasnier <fabrice.gasnier@...com>
Subject: [PATCH 5/5] serial: stm32: add RX and TX FIFO flush

Adds a flush of RX and TX FIFOs, and fixes some errors:
- adds RX FIFO flush in startup fonction
- removes the useless transmitter enabling in startup fonction
  (e.g. receiver only, see Documentation/serial/driver)
- configures FIFO threshold before enabling it, rather than after
- flushes both TX and RX in set_termios function

Signed-off-by: Erwan Le Ray <erwan.leray@...com>

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 4083145..21dc380 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -602,11 +602,11 @@ static int stm32_startup(struct uart_port *port)
 	if (ret)
 		return ret;
 
-	val = stm32_port->cr1_irq | USART_CR1_TE | USART_CR1_RE;
-	if (stm32_port->fifoen)
-		val |= USART_CR1_FIFOEN;
-	stm32_set_bits(port, ofs->cr1, val);
+	/* RX FIFO Flush */
+	if (ofs->rqr != UNDEF_REG)
+		stm32_set_bits(port, ofs->rqr, USART_RQR_RXFRQ);
 
+	/* Tx and RX FIFO configuration */
 	if (stm32_port->fifoen) {
 		val = readl_relaxed(port->membase + ofs->cr3);
 		val &= ~(USART_CR3_TXFTCFG_MASK | USART_CR3_RXFTCFG_MASK);
@@ -615,6 +615,12 @@ static int stm32_startup(struct uart_port *port)
 		writel_relaxed(val, port->membase + ofs->cr3);
 	}
 
+	/* RX FIFO enabling */
+	val = stm32_port->cr1_irq | USART_CR1_RE;
+	if (stm32_port->fifoen)
+		val |= USART_CR1_FIFOEN;
+	stm32_set_bits(port, ofs->cr1, val);
+
 	return 0;
 }
 
@@ -697,8 +703,12 @@ static void stm32_set_termios(struct uart_port *port, struct ktermios *termios,
 	/* Stop serial port and reset value */
 	writel_relaxed(0, port->membase + ofs->cr1);
 
-	cr1 = USART_CR1_TE | USART_CR1_RE;
+	/* flush RX & TX FIFO */
+	if (ofs->rqr != UNDEF_REG)
+		stm32_set_bits(port, ofs->rqr,
+			       USART_RQR_TXFRQ | USART_RQR_RXFRQ);
 
+	cr1 = USART_CR1_TE | USART_CR1_RE;
 	if (stm32_port->fifoen)
 		cr1 |= USART_CR1_FIFOEN;
 	cr2 = 0;
-- 
1.9.1