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Date:   Mon, 17 Feb 2020 14:08:01 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     "u.kleine-koenig@...gutronix.de" <u.kleine-koenig@...gutronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Schrempf Frieder <frieder.schrempf@...tron.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: [PATCH 1/2] serial: imx: ensure that RX irqs are off if RX is off

From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>

commit 76821e222c189b81d553b855ee7054340607eb46 upstream

Make sure that UCR1.RXDMAEN and UCR1.ATDMAEN (for the DMA case) and
UCR1.RRDYEN (for the PIO case) are off iff UCR1.RXEN is disabled. This
ensures that the fifo isn't read with RX disabled which results in an
exception.

Cc: <stable@...r.kernel.org> # v4.14.x
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
[Backport to v4.14]
Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
---
 drivers/tty/serial/imx.c | 116 ++++++++++++++++++++++++++-------------
 1 file changed, 78 insertions(+), 38 deletions(-)

diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
index a81a5be0cf7a..31e1e32c62c9 100644
--- a/drivers/tty/serial/imx.c
+++ b/drivers/tty/serial/imx.c
@@ -80,7 +80,7 @@
 #define UCR1_IDEN	(1<<12) /* Idle condition interrupt */
 #define UCR1_ICD_REG(x) (((x) & 3) << 10) /* idle condition detect */
 #define UCR1_RRDYEN	(1<<9)	/* Recv ready interrupt enable */
-#define UCR1_RDMAEN	(1<<8)	/* Recv ready DMA enable */
+#define UCR1_RXDMAEN	(1<<8)	/* Recv ready DMA enable */
 #define UCR1_IREN	(1<<7)	/* Infrared interface enable */
 #define UCR1_TXMPTYEN	(1<<6)	/* Transimitter empty interrupt enable */
 #define UCR1_RTSDEN	(1<<5)	/* RTS delta interrupt enable */
@@ -352,6 +352,30 @@ static void imx_port_rts_auto(struct imx_port *sport, unsigned long *ucr2)
 	*ucr2 |= UCR2_CTSC;
 }
 
+/*
+ * interrupts disabled on entry
+ */
+static void imx_start_rx(struct uart_port *port)
+{
+	struct imx_port *sport = (struct imx_port *)port;
+	unsigned int ucr1, ucr2;
+
+	ucr1 = readl(port->membase + UCR1);
+	ucr2 = readl(port->membase + UCR2);
+
+	ucr2 |= UCR2_RXEN;
+
+	if (sport->dma_is_enabled) {
+		ucr1 |= UCR1_RXDMAEN | UCR1_ATDMAEN;
+	} else {
+		ucr1 |= UCR1_RRDYEN;
+	}
+
+	/* Write UCR2 first as it includes RXEN */
+	writel(ucr2, port->membase + UCR2);
+	writel(ucr1, port->membase + UCR1);
+}
+
 /*
  * interrupts disabled on entry
  */
@@ -378,9 +402,10 @@ static void imx_stop_tx(struct uart_port *port)
 			imx_port_rts_active(sport, &temp);
 		else
 			imx_port_rts_inactive(sport, &temp);
-		temp |= UCR2_RXEN;
 		writel(temp, port->membase + UCR2);
 
+		imx_start_rx(port);
+
 		temp = readl(port->membase + UCR4);
 		temp &= ~UCR4_TCEN;
 		writel(temp, port->membase + UCR4);
@@ -393,7 +418,7 @@ static void imx_stop_tx(struct uart_port *port)
 static void imx_stop_rx(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
-	unsigned long temp;
+	unsigned long ucr1, ucr2;
 
 	if (sport->dma_is_enabled && sport->dma_is_rxing) {
 		if (sport->port.suspended) {
@@ -404,12 +429,18 @@ static void imx_stop_rx(struct uart_port *port)
 		}
 	}
 
-	temp = readl(sport->port.membase + UCR2);
-	writel(temp & ~UCR2_RXEN, sport->port.membase + UCR2);
+	ucr1 = readl(sport->port.membase + UCR1);
+	ucr2 = readl(sport->port.membase + UCR2);
 
-	/* disable the `Receiver Ready Interrrupt` */
-	temp = readl(sport->port.membase + UCR1);
-	writel(temp & ~UCR1_RRDYEN, sport->port.membase + UCR1);
+	if (sport->dma_is_enabled) {
+		ucr1 &= ~(UCR1_RXDMAEN | UCR1_ATDMAEN);
+	} else {
+		ucr1 &= ~UCR1_RRDYEN;
+	}
+	writel(ucr1, port->membase + UCR1);
+
+	ucr2 &= ~UCR2_RXEN;
+	writel(ucr2, port->membase + UCR2);
 }
 
 /*
@@ -581,10 +612,11 @@ static void imx_start_tx(struct uart_port *port)
 			imx_port_rts_active(sport, &temp);
 		else
 			imx_port_rts_inactive(sport, &temp);
-		if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
-			temp &= ~UCR2_RXEN;
 		writel(temp, port->membase + UCR2);
 
+		if (!(port->rs485.flags & SER_RS485_RX_DURING_TX))
+			imx_stop_rx(port);
+
 		/* enable transmitter and shifter empty irq */
 		temp = readl(port->membase + UCR4);
 		temp |= UCR4_TCEN;
@@ -1206,7 +1238,7 @@ static void imx_enable_dma(struct imx_port *sport)
 
 	/* set UCR1 */
 	temp = readl(sport->port.membase + UCR1);
-	temp |= UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN;
+	temp |= UCR1_RXDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN;
 	writel(temp, sport->port.membase + UCR1);
 
 	temp = readl(sport->port.membase + UCR2);
@@ -1224,7 +1256,7 @@ static void imx_disable_dma(struct imx_port *sport)
 
 	/* clear UCR1 */
 	temp = readl(sport->port.membase + UCR1);
-	temp &= ~(UCR1_RDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN);
+	temp &= ~(UCR1_RXDMAEN | UCR1_TDMAEN | UCR1_ATDMAEN);
 	writel(temp, sport->port.membase + UCR1);
 
 	/* clear UCR2 */
@@ -1289,11 +1321,9 @@ static int imx_startup(struct uart_port *port)
 	writel(USR1_RTSD | USR1_DTRD, sport->port.membase + USR1);
 	writel(USR2_ORE, sport->port.membase + USR2);
 
-	if (sport->dma_is_inited && !sport->dma_is_enabled)
-		imx_enable_dma(sport);
-
 	temp = readl(sport->port.membase + UCR1);
-	temp |= UCR1_RRDYEN | UCR1_UARTEN;
+	temp &= ~UCR1_RRDYEN;
+	temp |= UCR1_UARTEN;
 	if (sport->have_rtscts)
 			temp |= UCR1_RTSDEN;
 
@@ -1332,14 +1362,13 @@ static int imx_startup(struct uart_port *port)
 	 */
 	imx_enable_ms(&sport->port);
 
-	/*
-	 * Start RX DMA immediately instead of waiting for RX FIFO interrupts.
-	 * In our iMX53 the average delay for the first reception dropped from
-	 * approximately 35000 microseconds to 1000 microseconds.
-	 */
-	if (sport->dma_is_enabled) {
-		imx_disable_rx_int(sport);
+	if (sport->dma_is_inited) {
+		imx_enable_dma(sport);
 		start_rx_dma(sport);
+	} else {
+		temp = readl(sport->port.membase + UCR1);
+		temp |= UCR1_RRDYEN;
+		writel(temp, sport->port.membase + UCR1);
 	}
 
 	spin_unlock_irqrestore(&sport->port.lock, flags);
@@ -1386,7 +1415,8 @@ static void imx_shutdown(struct uart_port *port)
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 	temp = readl(sport->port.membase + UCR1);
-	temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN);
+	temp &= ~(UCR1_TXMPTYEN | UCR1_RRDYEN | UCR1_RTSDEN | UCR1_UARTEN |
+		  UCR1_RXDMAEN | UCR1_ATDMAEN);
 
 	writel(temp, sport->port.membase + UCR1);
 	spin_unlock_irqrestore(&sport->port.lock, flags);
@@ -1659,7 +1689,7 @@ static int imx_poll_init(struct uart_port *port)
 {
 	struct imx_port *sport = (struct imx_port *)port;
 	unsigned long flags;
-	unsigned long temp;
+	unsigned long ucr1, ucr2;
 	int retval;
 
 	retval = clk_prepare_enable(sport->clk_ipg);
@@ -1673,16 +1703,29 @@ static int imx_poll_init(struct uart_port *port)
 
 	spin_lock_irqsave(&sport->port.lock, flags);
 
-	temp = readl(sport->port.membase + UCR1);
+	/*
+	 * Be careful about the order of enabling bits here. First enable the
+	 * receiver (UARTEN + RXEN) and only then the corresponding irqs.
+	 * This prevents that a character that already sits in the RX fifo is
+	 * triggering an irq but the try to fetch it from there results in an
+	 * exception because UARTEN or RXEN is still off.
+	 */
+	ucr1 = readl(port->membase + UCR1);
+	ucr2 = readl(port->membase + UCR2);
+
 	if (is_imx1_uart(sport))
-		temp |= IMX1_UCR1_UARTCLKEN;
-	temp |= UCR1_UARTEN | UCR1_RRDYEN;
-	temp &= ~(UCR1_TXMPTYEN | UCR1_RTSDEN);
-	writel(temp, sport->port.membase + UCR1);
+		ucr1 |= IMX1_UCR1_UARTCLKEN;
 
-	temp = readl(sport->port.membase + UCR2);
-	temp |= UCR2_RXEN;
-	writel(temp, sport->port.membase + UCR2);
+	ucr1 |= UCR1_UARTEN;
+	ucr1 &= ~(UCR1_TXMPTYEN | UCR1_RTSDEN | UCR1_RRDYEN);
+
+	ucr2 |= UCR2_RXEN;
+
+	writel(ucr1, sport->port.membase + UCR1);
+	writel(ucr2, sport->port.membase + UCR2);
+
+	/* now enable irqs */
+	writel(ucr1 | UCR1_RRDYEN, sport->port.membase + UCR1);
 
 	spin_unlock_irqrestore(&sport->port.lock, flags);
 
@@ -1742,11 +1785,8 @@ static int imx_rs485_config(struct uart_port *port,
 
 	/* Make sure Rx is enabled in case Tx is active with Rx disabled */
 	if (!(rs485conf->flags & SER_RS485_ENABLED) ||
-	    rs485conf->flags & SER_RS485_RX_DURING_TX) {
-		temp = readl(sport->port.membase + UCR2);
-		temp |= UCR2_RXEN;
-		writel(temp, sport->port.membase + UCR2);
-	}
+	    rs485conf->flags & SER_RS485_RX_DURING_TX)
+		imx_start_rx(port);
 
 	port->rs485 = *rs485conf;
 
-- 
2.17.1

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