From 65ccffa95d1857e61340936bbba9a4e0a3cc004b Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@linutronix.de>
Date: Fri, 4 Feb 2022 16:01:17 +0106
Subject: [PATCH 21/63] serial: 8250: implement write_atomic

Implement a non-sleeping NMI-safe write_atomic() console function in
order to support atomic console printing during a panic.

Trasmitting data requires disabling interrupts. Since write_atomic()
can be called from any context, it may be called while another CPU
is executing in console code. In order to maintain the correct state
of the IER register, use the global cpu_sync to synchronize all
access to the IER register. This synchronization is only necessary
for serial ports that are being used as consoles.

The global cpu_sync is also used to synchronize between the write()
and write_atomic() callbacks. write() synchronizes per character,
write_atomic() synchronizes per line.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/8250/8250.h              |  41 ++++-
 drivers/tty/serial/8250/8250_aspeed_vuart.c |   2 +-
 drivers/tty/serial/8250/8250_bcm7271.c      |  21 ++-
 drivers/tty/serial/8250/8250_core.c         |  24 ++-
 drivers/tty/serial/8250/8250_exar.c         |   4 +-
 drivers/tty/serial/8250/8250_fsl.c          |   3 +-
 drivers/tty/serial/8250/8250_ingenic.c      |   3 +-
 drivers/tty/serial/8250/8250_mtk.c          |  32 +++-
 drivers/tty/serial/8250/8250_omap.c         |  18 +--
 drivers/tty/serial/8250/8250_port.c         | 160 ++++++++++++++++----
 drivers/tty/serial/8250/Kconfig             |   1 +
 include/linux/serial_8250.h                 |   5 +
 12 files changed, 265 insertions(+), 49 deletions(-)

diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h
index eeb7b43ebe53..b17715d340c3 100644
--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -176,12 +176,49 @@ static inline void serial_dl_write(struct uart_8250_port *up, int value)
 	up->dl_write(up, value);
 }
 
+static inline int serial8250_in_IER(struct uart_8250_port *up)
+{
+	struct uart_port *port = &up->port;
+	unsigned long flags;
+	bool is_console;
+	int ier;
+
+	is_console = uart_console(port);
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
+	ier = serial_in(up, UART_IER);
+
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
+
+	return ier;
+}
+
+static inline void serial8250_set_IER(struct uart_8250_port *up, int ier)
+{
+	struct uart_port *port = &up->port;
+	unsigned long flags;
+	bool is_console;
+
+	is_console = uart_console(port);
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
+	serial_out(up, UART_IER, ier);
+
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
+}
+
 static inline bool serial8250_set_THRI(struct uart_8250_port *up)
 {
 	if (up->ier & UART_IER_THRI)
 		return false;
 	up->ier |= UART_IER_THRI;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 	return true;
 }
 
@@ -190,7 +227,7 @@ static inline bool serial8250_clear_THRI(struct uart_8250_port *up)
 	if (!(up->ier & UART_IER_THRI))
 		return false;
 	up->ier &= ~UART_IER_THRI;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 	return true;
 }
 
diff --git a/drivers/tty/serial/8250/8250_aspeed_vuart.c b/drivers/tty/serial/8250/8250_aspeed_vuart.c
index 9d2a7856784f..7cc6b527c088 100644
--- a/drivers/tty/serial/8250/8250_aspeed_vuart.c
+++ b/drivers/tty/serial/8250/8250_aspeed_vuart.c
@@ -278,7 +278,7 @@ static void __aspeed_vuart_set_throttle(struct uart_8250_port *up,
 	up->ier &= ~irqs;
 	if (!throttle)
 		up->ier |= irqs;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 }
 static void aspeed_vuart_set_throttle(struct uart_port *port, bool throttle)
 {
diff --git a/drivers/tty/serial/8250/8250_bcm7271.c b/drivers/tty/serial/8250/8250_bcm7271.c
index a28f115f6194..2f2558e555e0 100644
--- a/drivers/tty/serial/8250/8250_bcm7271.c
+++ b/drivers/tty/serial/8250/8250_bcm7271.c
@@ -609,7 +609,7 @@ static int brcmuart_startup(struct uart_port *port)
 	 * will handle this.
 	 */
 	up->ier &= ~UART_IER_RDI;
-	serial_port_out(port, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	priv->tx_running = false;
 	priv->dma.rx_dma = NULL;
@@ -794,10 +794,12 @@ static int brcmuart_handle_irq(struct uart_port *p)
 	unsigned int iir = serial_port_in(p, UART_IIR);
 	struct brcmuart_priv *priv = p->private_data;
 	struct uart_8250_port *up = up_to_u8250p(p);
+	unsigned long cs_flags;
 	unsigned int status;
 	unsigned long flags;
 	unsigned int ier;
 	unsigned int mcr;
+	bool is_console;
 	int handled = 0;
 
 	/*
@@ -808,6 +810,10 @@ static int brcmuart_handle_irq(struct uart_port *p)
 		spin_lock_irqsave(&p->lock, flags);
 		status = serial_port_in(p, UART_LSR);
 		if ((status & UART_LSR_DR) == 0) {
+			is_console = uart_console(p);
+
+			if (is_console)
+				printk_cpu_sync_get_irqsave(cs_flags);
 
 			ier = serial_port_in(p, UART_IER);
 			/*
@@ -828,6 +834,9 @@ static int brcmuart_handle_irq(struct uart_port *p)
 				serial_port_in(p, UART_RX);
 			}
 
+			if (is_console)
+				printk_cpu_sync_put_irqrestore(cs_flags);
+
 			handled = 1;
 		}
 		spin_unlock_irqrestore(&p->lock, flags);
@@ -842,8 +851,10 @@ static enum hrtimer_restart brcmuart_hrtimer_func(struct hrtimer *t)
 	struct brcmuart_priv *priv = container_of(t, struct brcmuart_priv, hrt);
 	struct uart_port *p = priv->up;
 	struct uart_8250_port *up = up_to_u8250p(p);
+	unsigned long cs_flags;
 	unsigned int status;
 	unsigned long flags;
+	bool is_console;
 
 	if (priv->shutdown)
 		return HRTIMER_NORESTART;
@@ -865,12 +876,20 @@ static enum hrtimer_restart brcmuart_hrtimer_func(struct hrtimer *t)
 	/* re-enable receive unless upper layer has disabled it */
 	if ((up->ier & (UART_IER_RLSI | UART_IER_RDI)) ==
 	    (UART_IER_RLSI | UART_IER_RDI)) {
+		is_console = uart_console(p);
+
+		if (is_console)
+			printk_cpu_sync_get_irqsave(cs_flags);
+
 		status = serial_port_in(p, UART_IER);
 		status |= (UART_IER_RLSI | UART_IER_RDI);
 		serial_port_out(p, UART_IER, status);
 		status = serial_port_in(p, UART_MCR);
 		status |= UART_MCR_RTS;
 		serial_port_out(p, UART_MCR, status);
+
+		if (is_console)
+			printk_cpu_sync_put_irqrestore(cs_flags);
 	}
 	spin_unlock_irqrestore(&p->lock, flags);
 	return HRTIMER_NORESTART;
diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
index 81a5dab1a828..536f639ff56c 100644
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -255,8 +255,11 @@ static void serial8250_timeout(struct timer_list *t)
 static void serial8250_backup_timeout(struct timer_list *t)
 {
 	struct uart_8250_port *up = from_timer(up, t, timer);
+	struct uart_port *port = &up->port;
 	unsigned int iir, ier = 0, lsr;
+	unsigned long cs_flags;
 	unsigned long flags;
+	bool is_console;
 
 	spin_lock_irqsave(&up->port.lock, flags);
 
@@ -265,8 +268,16 @@ static void serial8250_backup_timeout(struct timer_list *t)
 	 * based handler.
 	 */
 	if (up->port.irq) {
+		is_console = uart_console(port);
+
+		if (is_console)
+			printk_cpu_sync_get_irqsave(cs_flags);
+
 		ier = serial_in(up, UART_IER);
 		serial_out(up, UART_IER, 0);
+
+		if (is_console)
+			printk_cpu_sync_put_irqrestore(cs_flags);
 	}
 
 	iir = serial_in(up, UART_IIR);
@@ -289,7 +300,7 @@ static void serial8250_backup_timeout(struct timer_list *t)
 		serial8250_tx_chars(up);
 
 	if (up->port.irq)
-		serial_out(up, UART_IER, ier);
+		serial8250_set_IER(up, ier);
 
 	spin_unlock_irqrestore(&up->port.lock, flags);
 
@@ -575,6 +586,14 @@ serial8250_register_ports(struct uart_driver *drv, struct device *dev)
 
 #ifdef CONFIG_SERIAL_8250_CONSOLE
 
+static void univ8250_console_write_atomic(struct console *co, const char *s,
+					  unsigned int count)
+{
+	struct uart_8250_port *up = &serial8250_ports[co->index];
+
+	serial8250_console_write_atomic(up, s, count);
+}
+
 static void univ8250_console_write(struct console *co, const char *s,
 				   unsigned int count)
 {
@@ -668,6 +687,7 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
 
 static struct console univ8250_console = {
 	.name		= "ttyS",
+	.write_atomic	= univ8250_console_write_atomic,
 	.write		= univ8250_console_write,
 	.device		= uart_console_device,
 	.setup		= univ8250_console_setup,
@@ -961,7 +981,7 @@ static void serial_8250_overrun_backoff_work(struct work_struct *work)
 	spin_lock_irqsave(&port->lock, flags);
 	up->ier |= UART_IER_RLSI | UART_IER_RDI;
 	up->port.read_status_mask |= UART_LSR_DR;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 	spin_unlock_irqrestore(&port->lock, flags);
 }
 
diff --git a/drivers/tty/serial/8250/8250_exar.c b/drivers/tty/serial/8250/8250_exar.c
index b5ae6ec61c9f..20875e783909 100644
--- a/drivers/tty/serial/8250/8250_exar.c
+++ b/drivers/tty/serial/8250/8250_exar.c
@@ -231,6 +231,8 @@ static void xr17v35x_set_divisor(struct uart_port *p, unsigned int baud,
 
 static int xr17v35x_startup(struct uart_port *port)
 {
+	struct uart_8250_port *up = up_to_u8250p(port);
+
 	/*
 	 * First enable access to IER [7:5], ISR [5:4], FCR [5:4],
 	 * MCR [7:5] and MSR [7:0]
@@ -241,7 +243,7 @@ static int xr17v35x_startup(struct uart_port *port)
 	 * Make sure all interrups are masked until initialization is
 	 * complete and the FIFOs are cleared
 	 */
-	serial_port_out(port, UART_IER, 0);
+	serial8250_set_IER(up, 0);
 
 	return serial8250_do_startup(port);
 }
diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c
index 8adfaa183f77..eaf148245a10 100644
--- a/drivers/tty/serial/8250/8250_fsl.c
+++ b/drivers/tty/serial/8250/8250_fsl.c
@@ -58,7 +58,8 @@ int fsl8250_handle_irq(struct uart_port *port)
 	if ((orig_lsr & UART_LSR_OE) && (up->overrun_backoff_time_ms > 0)) {
 		unsigned long delay;
 
-		up->ier = port->serial_in(port, UART_IER);
+		up->ier = serial8250_in_IER(up);
+
 		if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {
 			port->ops->stop_rx(port);
 		} else {
diff --git a/drivers/tty/serial/8250/8250_ingenic.c b/drivers/tty/serial/8250/8250_ingenic.c
index 2b2f5d8d24b9..2b78e6c394fb 100644
--- a/drivers/tty/serial/8250/8250_ingenic.c
+++ b/drivers/tty/serial/8250/8250_ingenic.c
@@ -146,6 +146,7 @@ OF_EARLYCON_DECLARE(x1000_uart, "ingenic,x1000-uart",
 
 static void ingenic_uart_serial_out(struct uart_port *p, int offset, int value)
 {
+	struct uart_8250_port *up = up_to_u8250p(p);
 	int ier;
 
 	switch (offset) {
@@ -167,7 +168,7 @@ static void ingenic_uart_serial_out(struct uart_port *p, int offset, int value)
 		 * If we have enabled modem status IRQs we should enable
 		 * modem mode.
 		 */
-		ier = p->serial_in(p, UART_IER);
+		ier = serial8250_in_IER(up);
 
 		if (ier & UART_IER_MSI)
 			value |= UART_MCR_MDCE | UART_MCR_FCM;
diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c
index 295b9ba1b4f3..a5bb7c7a6441 100644
--- a/drivers/tty/serial/8250/8250_mtk.c
+++ b/drivers/tty/serial/8250/8250_mtk.c
@@ -226,12 +226,40 @@ static void mtk8250_shutdown(struct uart_port *port)
 
 static void mtk8250_disable_intrs(struct uart_8250_port *up, int mask)
 {
-	serial_out(up, UART_IER, serial_in(up, UART_IER) & (~mask));
+	struct uart_port *port = &up->port;
+	unsigned long flags;
+	bool is_console;
+	int ier;
+
+	is_console = uart_console(port);
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
+	ier = serial_in(up, UART_IER);
+	serial_out(up, UART_IER, ier & (~mask));
+
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
 }
 
 static void mtk8250_enable_intrs(struct uart_8250_port *up, int mask)
 {
-	serial_out(up, UART_IER, serial_in(up, UART_IER) | mask);
+	struct uart_port *port = &up->port;
+	unsigned long flags;
+	bool is_console;
+	int ier;
+
+	is_console = uart_console(port);
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
+	ier = serial_in(up, UART_IER);
+	serial_out(up, UART_IER, ier | mask);
+
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
 }
 
 static void mtk8250_set_flow_ctrl(struct uart_8250_port *up, int mode)
diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index a3eaf293f204..034f430203c9 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -334,7 +334,7 @@ static void omap8250_restore_regs(struct uart_8250_port *up)
 	/* drop TCR + TLR access, we setup XON/XOFF later */
 	serial8250_out_MCR(up, mcr);
 
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
 	serial_dl_write(up, priv->quot);
@@ -524,7 +524,7 @@ static void omap_8250_pm(struct uart_port *port, unsigned int state,
 	serial_out(up, UART_EFR, efr | UART_EFR_ECB);
 	serial_out(up, UART_LCR, 0);
 
-	serial_out(up, UART_IER, (state != 0) ? UART_IERX_SLEEP : 0);
+	serial8250_set_IER(up, (state != 0) ? UART_IERX_SLEEP : 0);
 	serial_out(up, UART_LCR, UART_LCR_CONF_MODE_B);
 	serial_out(up, UART_EFR, efr);
 	serial_out(up, UART_LCR, 0);
@@ -719,7 +719,7 @@ static int omap_8250_startup(struct uart_port *port)
 		goto err;
 
 	up->ier = UART_IER_RLSI | UART_IER_RDI;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 #ifdef CONFIG_PM
 	up->capabilities |= UART_CAP_RPM;
@@ -760,7 +760,7 @@ static void omap_8250_shutdown(struct uart_port *port)
 		serial_out(up, UART_OMAP_EFR2, 0x0);
 
 	up->ier = 0;
-	serial_out(up, UART_IER, 0);
+	serial8250_set_IER(up, 0);
 
 	if (up->dma)
 		serial8250_release_dma(up);
@@ -808,7 +808,7 @@ static void omap_8250_unthrottle(struct uart_port *port)
 		up->dma->rx_dma(up);
 	up->ier |= UART_IER_RLSI | UART_IER_RDI;
 	port->read_status_mask |= UART_LSR_DR;
-	serial_out(up, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	pm_runtime_mark_last_busy(port->dev);
@@ -899,7 +899,7 @@ static void __dma_rx_complete(void *param)
 	__dma_rx_do_complete(p);
 	if (!priv->throttled) {
 		p->ier |= UART_IER_RLSI | UART_IER_RDI;
-		serial_out(p, UART_IER, p->ier);
+		serial8250_set_IER(p, p->ier);
 		if (!(priv->habit & UART_HAS_EFR2))
 			omap_8250_rx_dma(p);
 	}
@@ -956,7 +956,7 @@ static int omap_8250_rx_dma(struct uart_8250_port *p)
 			 * callback to run.
 			 */
 			p->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
-			serial_out(p, UART_IER, p->ier);
+			serial8250_set_IER(p, p->ier);
 		}
 		goto out;
 	}
@@ -1169,12 +1169,12 @@ static void am654_8250_handle_rx_dma(struct uart_8250_port *up, u8 iir,
 		 * periodic timeouts, re-enable interrupts.
 		 */
 		up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
-		serial_out(up, UART_IER, up->ier);
+		serial8250_set_IER(up, up->ier);
 		omap_8250_rx_dma_flush(up);
 		serial_in(up, UART_IIR);
 		serial_out(up, UART_OMAP_EFR2, 0x0);
 		up->ier |= UART_IER_RLSI | UART_IER_RDI;
-		serial_out(up, UART_IER, up->ier);
+		serial8250_set_IER(up, up->ier);
 	}
 }
 
diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index c744feabd7cd..975c16267196 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -744,7 +744,7 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
 			serial_out(p, UART_EFR, UART_EFR_ECB);
 			serial_out(p, UART_LCR, 0);
 		}
-		serial_out(p, UART_IER, sleep ? UART_IERX_SLEEP : 0);
+		serial8250_set_IER(p, sleep ? UART_IERX_SLEEP : 0);
 		if (p->capabilities & UART_CAP_EFR) {
 			serial_out(p, UART_LCR, UART_LCR_CONF_MODE_B);
 			serial_out(p, UART_EFR, efr);
@@ -755,12 +755,29 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
 	serial8250_rpm_put(p);
 }
 
-static void serial8250_clear_IER(struct uart_8250_port *up)
+static unsigned int serial8250_clear_IER(struct uart_8250_port *up)
 {
+	struct uart_port *port = &up->port;
+	unsigned int clearval = 0;
+	unsigned long flags;
+	bool is_console;
+	unsigned int prior;
+
+	is_console = uart_console(port);
+
 	if (up->capabilities & UART_CAP_UUE)
-		serial_out(up, UART_IER, UART_IER_UUE);
-	else
-		serial_out(up, UART_IER, 0);
+		clearval = UART_IER_UUE;
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
+	prior = serial_in(up, UART_IER);
+	serial_out(up, UART_IER, clearval);
+
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
+
+	return prior;
 }
 
 #ifdef CONFIG_SERIAL_8250_RSA
@@ -1026,8 +1043,11 @@ static int broken_efr(struct uart_8250_port *up)
  */
 static void autoconfig_16550a(struct uart_8250_port *up)
 {
+	struct uart_port *port = &up->port;
 	unsigned char status1, status2;
 	unsigned int iersave;
+	unsigned long flags;
+	bool is_console;
 
 	up->port.type = PORT_16550A;
 	up->capabilities |= UART_CAP_FIFO;
@@ -1139,6 +1159,11 @@ static void autoconfig_16550a(struct uart_8250_port *up)
 		return;
 	}
 
+	is_console = uart_console(port);
+
+	if (is_console)
+		printk_cpu_sync_get_irqsave(flags);
+
 	/*
 	 * Try writing and reading the UART_IER_UUE bit (b6).
 	 * If it works, this is probably one of the Xscale platform's
@@ -1174,6 +1199,9 @@ static void autoconfig_16550a(struct uart_8250_port *up)
 	}
 	serial_out(up, UART_IER, iersave);
 
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(flags);
+
 	/*
 	 * We distinguish between 16550A and U6 16550A by counting
 	 * how many bytes are in the FIFO.
@@ -1196,8 +1224,10 @@ static void autoconfig(struct uart_8250_port *up)
 	unsigned char status1, scratch, scratch2, scratch3;
 	unsigned char save_lcr, save_mcr;
 	struct uart_port *port = &up->port;
+	unsigned long cs_flags;
 	unsigned long flags;
 	unsigned int old_capabilities;
+	bool is_console;
 
 	if (!port->iobase && !port->mapbase && !port->membase)
 		return;
@@ -1215,6 +1245,11 @@ static void autoconfig(struct uart_8250_port *up)
 	up->bugs = 0;
 
 	if (!(port->flags & UPF_BUGGY_UART)) {
+		is_console = uart_console(port);
+
+		if (is_console)
+			printk_cpu_sync_get_irqsave(cs_flags);
+
 		/*
 		 * Do a simple existence test first; if we fail this,
 		 * there's no point trying anything else.
@@ -1244,6 +1279,10 @@ static void autoconfig(struct uart_8250_port *up)
 #endif
 		scratch3 = serial_in(up, UART_IER) & 0x0f;
 		serial_out(up, UART_IER, scratch);
+
+		if (is_console)
+			printk_cpu_sync_put_irqrestore(cs_flags);
+
 		if (scratch2 != 0 || scratch3 != 0x0F) {
 			/*
 			 * We failed; there's nothing here
@@ -1367,7 +1406,9 @@ static void autoconfig_irq(struct uart_8250_port *up)
 	unsigned char save_mcr, save_ier;
 	unsigned char save_ICP = 0;
 	unsigned int ICP = 0;
+	unsigned long flags;
 	unsigned long irqs;
+	bool is_console;
 	int irq;
 
 	if (port->flags & UPF_FOURPORT) {
@@ -1377,6 +1418,13 @@ static void autoconfig_irq(struct uart_8250_port *up)
 		inb_p(ICP);
 	}
 
+	is_console = uart_console(port);
+
+	if (is_console) {
+		console_lock();
+		printk_cpu_sync_get_irqsave(flags);
+	}
+
 	/* forget possible initially masked and pending IRQ */
 	probe_irq_off(probe_irq_on());
 	save_mcr = serial8250_in_MCR(up);
@@ -1407,6 +1455,11 @@ static void autoconfig_irq(struct uart_8250_port *up)
 	if (port->flags & UPF_FOURPORT)
 		outb_p(save_ICP, ICP);
 
+	if (is_console) {
+		printk_cpu_sync_put_irqrestore(flags);
+		console_unlock();
+	}
+
 	port->irq = (irq > 0) ? irq : 0;
 }
 
@@ -1418,7 +1471,7 @@ static void serial8250_stop_rx(struct uart_port *port)
 
 	up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
 	up->port.read_status_mask &= ~UART_LSR_DR;
-	serial_port_out(port, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	serial8250_rpm_put(up);
 }
@@ -1448,7 +1501,7 @@ void serial8250_em485_stop_tx(struct uart_8250_port *p)
 		serial8250_clear_and_reinit_fifos(p);
 
 		p->ier |= UART_IER_RLSI | UART_IER_RDI;
-		serial_port_out(&p->port, UART_IER, p->ier);
+		serial8250_set_IER(p, p->ier);
 	}
 }
 EXPORT_SYMBOL_GPL(serial8250_em485_stop_tx);
@@ -1697,7 +1750,7 @@ static void serial8250_disable_ms(struct uart_port *port)
 	mctrl_gpio_disable_ms(up->gpios);
 
 	up->ier &= ~UART_IER_MSI;
-	serial_port_out(port, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 }
 
 static void serial8250_enable_ms(struct uart_port *port)
@@ -1713,7 +1766,7 @@ static void serial8250_enable_ms(struct uart_port *port)
 	up->ier |= UART_IER_MSI;
 
 	serial8250_rpm_get(up);
-	serial_port_out(port, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 	serial8250_rpm_put(up);
 }
 
@@ -2168,8 +2221,7 @@ static void serial8250_put_poll_char(struct uart_port *port,
 	/*
 	 *	First save the IER then disable the interrupts
 	 */
-	ier = serial_port_in(port, UART_IER);
-	serial8250_clear_IER(up);
+	ier = serial8250_clear_IER(up);
 
 	wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
 	/*
@@ -2182,7 +2234,7 @@ static void serial8250_put_poll_char(struct uart_port *port,
 	 *	and restore the IER
 	 */
 	wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
-	serial_port_out(port, UART_IER, ier);
+	serial8250_set_IER(up, ier);
 	serial8250_rpm_put(up);
 }
 
@@ -2191,8 +2243,10 @@ static void serial8250_put_poll_char(struct uart_port *port,
 int serial8250_do_startup(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
+	unsigned long cs_flags;
 	unsigned long flags;
 	unsigned char iir;
+	bool is_console;
 	int retval;
 	u16 lsr;
 
@@ -2213,7 +2267,7 @@ int serial8250_do_startup(struct uart_port *port)
 		up->acr = 0;
 		serial_port_out(port, UART_LCR, UART_LCR_CONF_MODE_B);
 		serial_port_out(port, UART_EFR, UART_EFR_ECB);
-		serial_port_out(port, UART_IER, 0);
+		serial8250_set_IER(up, 0);
 		serial_port_out(port, UART_LCR, 0);
 		serial_icr_write(up, UART_CSR, 0); /* Reset the UART */
 		serial_port_out(port, UART_LCR, UART_LCR_CONF_MODE_B);
@@ -2223,7 +2277,7 @@ int serial8250_do_startup(struct uart_port *port)
 
 	if (port->type == PORT_DA830) {
 		/* Reset the port */
-		serial_port_out(port, UART_IER, 0);
+		serial8250_set_IER(up, 0);
 		serial_port_out(port, UART_DA830_PWREMU_MGMT, 0);
 		mdelay(10);
 
@@ -2322,6 +2376,8 @@ int serial8250_do_startup(struct uart_port *port)
 	if (retval)
 		goto out;
 
+	is_console = uart_console(port);
+
 	if (port->irq && !(up->port.flags & UPF_NO_THRE_TEST)) {
 		unsigned char iir1;
 
@@ -2338,6 +2394,9 @@ int serial8250_do_startup(struct uart_port *port)
 		 */
 		spin_lock_irqsave(&port->lock, flags);
 
+		if (is_console)
+			printk_cpu_sync_get_irqsave(cs_flags);
+
 		wait_for_xmitr(up, UART_LSR_THRE);
 		serial_port_out_sync(port, UART_IER, UART_IER_THRI);
 		udelay(1); /* allow THRE to set */
@@ -2348,6 +2407,9 @@ int serial8250_do_startup(struct uart_port *port)
 		iir = serial_port_in(port, UART_IIR);
 		serial_port_out(port, UART_IER, 0);
 
+		if (is_console)
+			printk_cpu_sync_put_irqrestore(cs_flags);
+
 		spin_unlock_irqrestore(&port->lock, flags);
 
 		if (port->irqflags & IRQF_SHARED)
@@ -2402,10 +2464,14 @@ int serial8250_do_startup(struct uart_port *port)
 	 * Do a quick test to see if we receive an interrupt when we enable
 	 * the TX irq.
 	 */
+	if (is_console)
+		printk_cpu_sync_get_irqsave(cs_flags);
 	serial_port_out(port, UART_IER, UART_IER_THRI);
 	lsr = serial_port_in(port, UART_LSR);
 	iir = serial_port_in(port, UART_IIR);
 	serial_port_out(port, UART_IER, 0);
+	if (is_console)
+		printk_cpu_sync_put_irqrestore(cs_flags);
 
 	if (lsr & UART_LSR_TEMT && iir & UART_IIR_NO_INT) {
 		if (!(up->bugs & UART_BUG_TXEN)) {
@@ -2437,7 +2503,7 @@ int serial8250_do_startup(struct uart_port *port)
 	if (up->dma) {
 		const char *msg = NULL;
 
-		if (uart_console(port))
+		if (is_console)
 			msg = "forbid DMA for kernel console";
 		else if (serial8250_request_dma(up))
 			msg = "failed to request DMA";
@@ -2488,7 +2554,7 @@ void serial8250_do_shutdown(struct uart_port *port)
 	 */
 	spin_lock_irqsave(&port->lock, flags);
 	up->ier = 0;
-	serial_port_out(port, UART_IER, 0);
+	serial8250_set_IER(up, 0);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	synchronize_irq(port->irq);
@@ -2850,7 +2916,7 @@ serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios,
 	if (up->capabilities & UART_CAP_RTOIE)
 		up->ier |= UART_IER_RTOIE;
 
-	serial_port_out(port, UART_IER, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	if (up->capabilities & UART_CAP_EFR) {
 		unsigned char efr = 0;
@@ -3315,7 +3381,7 @@ EXPORT_SYMBOL_GPL(serial8250_set_defaults);
 
 #ifdef CONFIG_SERIAL_8250_CONSOLE
 
-static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
+static void serial8250_console_putchar_locked(struct uart_port *port, unsigned char ch)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 
@@ -3323,6 +3389,18 @@ static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
 	serial_port_out(port, UART_TX, ch);
 }
 
+static void serial8250_console_putchar(struct uart_port *port, unsigned char ch)
+{
+	struct uart_8250_port *up = up_to_u8250p(port);
+	unsigned long flags;
+
+	wait_for_xmitr(up, UART_LSR_THRE);
+
+	printk_cpu_sync_get_irqsave(flags);
+	serial8250_console_putchar_locked(port, ch);
+	printk_cpu_sync_put_irqrestore(flags);
+}
+
 /*
  *	Restore serial console when h/w power-off detected
  */
@@ -3349,6 +3427,32 @@ static void serial8250_console_restore(struct uart_8250_port *up)
 	serial8250_out_MCR(up, up->mcr | UART_MCR_DTR | UART_MCR_RTS);
 }
 
+void serial8250_console_write_atomic(struct uart_8250_port *up,
+				     const char *s, unsigned int count)
+{
+	struct uart_port *port = &up->port;
+	unsigned long flags;
+	unsigned int ier;
+
+	printk_cpu_sync_get_irqsave(flags);
+
+	touch_nmi_watchdog();
+
+	ier = serial8250_clear_IER(up);
+
+	if (atomic_fetch_inc(&up->console_printing)) {
+		uart_console_write(port, "\n", 1,
+				   serial8250_console_putchar_locked);
+	}
+	uart_console_write(port, s, count, serial8250_console_putchar_locked);
+	atomic_dec(&up->console_printing);
+
+	wait_for_xmitr(up, UART_LSR_BOTH_EMPTY);
+	serial8250_set_IER(up, ier);
+
+	printk_cpu_sync_put_irqrestore(flags);
+}
+
 /*
  * Print a string to the serial port using the device FIFO
  *
@@ -3394,20 +3498,15 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 	struct uart_port *port = &up->port;
 	unsigned long flags;
 	unsigned int ier, use_fifo;
-	int locked = 1;
 
 	touch_nmi_watchdog();
 
-	if (oops_in_progress)
-		locked = spin_trylock_irqsave(&port->lock, flags);
-	else
-		spin_lock_irqsave(&port->lock, flags);
+	spin_lock_irqsave(&port->lock, flags);
 
 	/*
 	 *	First save the IER then disable the interrupts
 	 */
-	ier = serial_port_in(port, UART_IER);
-	serial8250_clear_IER(up);
+	ier = serial8250_clear_IER(up);
 
 	/* check scratch reg to see if port powered off during system sleep */
 	if (up->canary && (up->canary != serial_port_in(port, UART_SCR))) {
@@ -3441,10 +3540,12 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 		 */
 		!(up->port.flags & UPF_CONS_FLOW);
 
+	atomic_inc(&up->console_printing);
 	if (likely(use_fifo))
 		serial8250_console_fifo_write(up, s, count);
 	else
 		uart_console_write(port, s, count, serial8250_console_putchar);
+	atomic_dec(&up->console_printing);
 
 	/*
 	 *	Finally, wait for transmitter to become empty
@@ -3457,8 +3558,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 		if (em485->tx_stopped)
 			up->rs485_stop_tx(up);
 	}
-
-	serial_port_out(port, UART_IER, ier);
+	serial8250_set_IER(up, ier);
 
 	/*
 	 *	The receive handling will happen properly because the
@@ -3470,8 +3570,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s,
 	if (up->msr_saved_flags)
 		serial8250_modem_status(up);
 
-	if (locked)
-		spin_unlock_irqrestore(&port->lock, flags);
+	spin_unlock_irqrestore(&port->lock, flags);
 }
 
 static unsigned int probe_baud(struct uart_port *port)
@@ -3491,6 +3590,7 @@ static unsigned int probe_baud(struct uart_port *port)
 
 int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
 {
+	struct uart_8250_port *up = up_to_u8250p(port);
 	int baud = 9600;
 	int bits = 8;
 	int parity = 'n';
@@ -3500,6 +3600,8 @@ int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
 	if (!port->iobase && !port->membase)
 		return -ENODEV;
 
+	atomic_set(&up->console_printing, 0);
+
 	if (options)
 		uart_parse_options(options, &baud, &parity, &bits, &flow);
 	else if (probe)
diff --git a/drivers/tty/serial/8250/Kconfig b/drivers/tty/serial/8250/Kconfig
index 583a340f9934..1f31320820a6 100644
--- a/drivers/tty/serial/8250/Kconfig
+++ b/drivers/tty/serial/8250/Kconfig
@@ -9,6 +9,7 @@ config SERIAL_8250
 	depends on !S390
 	select SERIAL_CORE
 	select SERIAL_MCTRL_GPIO if GPIOLIB
+	select HAVE_ATOMIC_CONSOLE
 	help
 	  This selects whether you want to include the driver for the standard
 	  serial ports.  The standard answer is Y.  People who might say N
diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h
index 79b328861c5f..35f44352e641 100644
--- a/include/linux/serial_8250.h
+++ b/include/linux/serial_8250.h
@@ -7,6 +7,7 @@
 #ifndef _LINUX_SERIAL_8250_H
 #define _LINUX_SERIAL_8250_H
 
+#include <linux/atomic.h>
 #include <linux/serial_core.h>
 #include <linux/serial_reg.h>
 #include <linux/platform_device.h>
@@ -124,6 +125,8 @@ struct uart_8250_port {
 #define MSR_SAVE_FLAGS UART_MSR_ANY_DELTA
 	unsigned char		msr_saved_flags;
 
+	atomic_t		console_printing;
+
 	struct uart_8250_dma	*dma;
 	const struct uart_8250_ops *ops;
 
@@ -179,6 +182,8 @@ void serial8250_init_port(struct uart_8250_port *up);
 void serial8250_set_defaults(struct uart_8250_port *up);
 void serial8250_console_write(struct uart_8250_port *up, const char *s,
 			      unsigned int count);
+void serial8250_console_write_atomic(struct uart_8250_port *up, const char *s,
+				     unsigned int count);
 int serial8250_console_setup(struct uart_port *port, char *options, bool probe);
 int serial8250_console_exit(struct uart_port *port);
 
-- 
2.46.0

