path: root/debian/patches-rt/serial-8250-only-atomic-lock-for-console.patch

From: John Ogness <john.ogness@linutronix.de>
Date: Fri, 10 Jan 2020 16:45:31 +0106
Subject: [PATCH] serial: 8250: only atomic lock for console
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.4/older/patches-5.4.17-rt8.tar.xz

The atomic console implementation requires that IER is synchronized
between atomic and non-atomic usage. However, it was implemented such
that the console_atomic_lock was performed for all IER access, even
if that port was not a console.

The implementation also used a usage counter to keep track of IER
clear/restore windows. However, this is not needed because the
console_atomic_lock synchronization of IER access with prevent any
situations where IER is prematurely restored or left cleared.

Move the IER access functions to inline macros. They will only
console_atomic_lock if the port is a console. Remove the
restore_ier() function by having clear_ier() return the prior IER
value so that the caller can restore it using set_ier(). Rename the
IER access functions to match other 8250 wrapper macros.

Suggested-by: Dick Hollenbeck <dick@softplc.com>
Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/tty/serial/8250/8250.h      |   65 +++++++++++++++++++---------
 drivers/tty/serial/8250/8250_core.c |    6 +-
 drivers/tty/serial/8250/8250_dma.c  |    4 -
 drivers/tty/serial/8250/8250_port.c |   81 ++++++++----------------------------
 4 files changed, 66 insertions(+), 90 deletions(-)

--- a/drivers/tty/serial/8250/8250.h
+++ b/drivers/tty/serial/8250/8250.h
@@ -96,10 +96,6 @@ struct serial8250_config {
 #define SERIAL8250_SHARE_IRQS 0
 #endif
 
-void set_ier(struct uart_8250_port *up, unsigned char ier);
-void clear_ier(struct uart_8250_port *up);
-void restore_ier(struct uart_8250_port *up);
-
 #define SERIAL8250_PORT_FLAGS(_base, _irq, _flags)		\
 	{							\
 		.iobase		= _base,			\
@@ -134,39 +130,64 @@ static inline void serial_dl_write(struc
 	up->dl_write(up, value);
 }
 
-static inline bool serial8250_set_THRI(struct uart_8250_port *up)
+static inline void serial8250_set_IER(struct uart_8250_port *up,
+				      unsigned char ier)
 {
-	if (up->ier & UART_IER_THRI)
-		return false;
-	up->ier |= UART_IER_THRI;
-	serial_out(up, UART_IER, up->ier);
-	return true;
+	struct uart_port *port = &up->port;
+	unsigned int flags;
+	bool is_console;
+
+	is_console = uart_console(port);
+
+	if (is_console)
+		console_atomic_lock(&flags);
+
+	serial_out(up, UART_IER, ier);
+
+	if (is_console)
+		console_atomic_unlock(flags);
 }
 
-static inline bool serial8250_set_THRI_sier(struct uart_8250_port *up)
+static inline unsigned char serial8250_clear_IER(struct uart_8250_port *up)
 {
-	if (up->ier & UART_IER_THRI)
-		return false;
-	up->ier |= UART_IER_THRI;
-	set_ier(up, up->ier);
-	return true;
+	struct uart_port *port = &up->port;
+	unsigned int clearval = 0;
+	unsigned int prior;
+	unsigned int flags;
+	bool is_console;
+
+	is_console = uart_console(port);
+
+	if (up->capabilities & UART_CAP_UUE)
+		clearval = UART_IER_UUE;
+
+	if (is_console)
+		console_atomic_lock(&flags);
+
+	prior = serial_port_in(port, UART_IER);
+	serial_port_out(port, UART_IER, clearval);
+
+	if (is_console)
+		console_atomic_unlock(flags);
+
+	return prior;
 }
 
-static inline bool serial8250_clear_THRI(struct uart_8250_port *up)
+static inline bool serial8250_set_THRI(struct uart_8250_port *up)
 {
-	if (!(up->ier & UART_IER_THRI))
+	if (up->ier & UART_IER_THRI)
 		return false;
-	up->ier &= ~UART_IER_THRI;
-	serial_out(up, UART_IER, up->ier);
+	up->ier |= UART_IER_THRI;
+	serial8250_set_IER(up, up->ier);
 	return true;
 }
 
-static inline bool serial8250_clear_THRI_sier(struct uart_8250_port *up)
+static inline bool serial8250_clear_THRI(struct uart_8250_port *up)
 {
 	if (!(up->ier & UART_IER_THRI))
 		return false;
 	up->ier &= ~UART_IER_THRI;
-	set_ier(up, up->ier);
+	serial8250_set_IER(up, up->ier);
 	return true;
 }
 
--- a/drivers/tty/serial/8250/8250_core.c
+++ b/drivers/tty/serial/8250/8250_core.c
@@ -266,7 +266,7 @@ static void serial8250_timeout(struct ti
 static void serial8250_backup_timeout(struct timer_list *t)
 {
 	struct uart_8250_port *up = from_timer(up, t, timer);
-	unsigned int iir, lsr;
+	unsigned int iir, ier = 0, lsr;
 	unsigned long flags;
 
 	spin_lock_irqsave(&up->port.lock, flags);
@@ -276,7 +276,7 @@ static void serial8250_backup_timeout(st
 	 * based handler.
 	 */
 	if (up->port.irq)
-		clear_ier(up);
+		ier = serial8250_clear_IER(up);
 
 	iir = serial_in(up, UART_IIR);
 
@@ -299,7 +299,7 @@ static void serial8250_backup_timeout(st
 		serial8250_tx_chars(up);
 
 	if (up->port.irq)
-		restore_ier(up);
+		serial8250_set_IER(up, ier);
 
 	spin_unlock_irqrestore(&up->port.lock, flags);
 
--- a/drivers/tty/serial/8250/8250_dma.c
+++ b/drivers/tty/serial/8250/8250_dma.c
@@ -35,7 +35,7 @@ static void __dma_tx_complete(void *para
 
 	ret = serial8250_tx_dma(p);
 	if (ret)
-		serial8250_set_THRI_sier(p);
+		serial8250_set_THRI(p);
 
 	spin_unlock_irqrestore(&p->port.lock, flags);
 }
@@ -98,7 +98,7 @@ int serial8250_tx_dma(struct uart_8250_p
 	dma_async_issue_pending(dma->txchan);
 	if (dma->tx_err) {
 		dma->tx_err = 0;
-		serial8250_clear_THRI_sier(p);
+		serial8250_clear_THRI(p);
 	}
 	return 0;
 err:
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -721,7 +721,7 @@ static void serial8250_set_sleep(struct
 			serial_out(p, UART_EFR, UART_EFR_ECB);
 			serial_out(p, UART_LCR, 0);
 		}
-		set_ier(p, 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);
@@ -1390,7 +1390,7 @@ static void serial8250_stop_rx(struct ua
 
 	up->ier &= ~(UART_IER_RLSI | UART_IER_RDI);
 	up->port.read_status_mask &= ~UART_LSR_DR;
-	set_ier(up, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	serial8250_rpm_put(up);
 }
@@ -1408,7 +1408,7 @@ static void __do_stop_tx_rs485(struct ua
 		serial8250_clear_and_reinit_fifos(p);
 
 		p->ier |= UART_IER_RLSI | UART_IER_RDI;
-		set_ier(p, p->ier);
+		serial8250_set_IER(p, p->ier);
 	}
 }
 static enum hrtimer_restart serial8250_em485_handle_stop_tx(struct hrtimer *t)
@@ -1459,7 +1459,7 @@ static void __stop_tx_rs485(struct uart_
 
 static inline void __do_stop_tx(struct uart_8250_port *p)
 {
-	if (serial8250_clear_THRI_sier(p))
+	if (serial8250_clear_THRI(p))
 		serial8250_rpm_put_tx(p);
 }
 
@@ -1509,7 +1509,7 @@ static inline void __start_tx(struct uar
 	if (up->dma && !up->dma->tx_dma(up))
 		return;
 
-	if (serial8250_set_THRI_sier(up)) {
+	if (serial8250_set_THRI(up)) {
 		if (up->bugs & UART_BUG_TXEN) {
 			unsigned char lsr;
 
@@ -1616,7 +1616,7 @@ static void serial8250_disable_ms(struct
 	mctrl_gpio_disable_ms(up->gpios);
 
 	up->ier &= ~UART_IER_MSI;
-	set_ier(up, up->ier);
+	serial8250_set_IER(up, up->ier);
 }
 
 static void serial8250_enable_ms(struct uart_port *port)
@@ -1632,7 +1632,7 @@ static void serial8250_enable_ms(struct
 	up->ier |= UART_IER_MSI;
 
 	serial8250_rpm_get(up);
-	set_ier(up, up->ier);
+	serial8250_set_IER(up, up->ier);
 	serial8250_rpm_put(up);
 }
 
@@ -1991,54 +1991,6 @@ static void wait_for_xmitr(struct uart_8
 	}
 }
 
-static atomic_t ier_counter = ATOMIC_INIT(0);
-static atomic_t ier_value = ATOMIC_INIT(0);
-
-void set_ier(struct uart_8250_port *up, unsigned char ier)
-{
-	struct uart_port *port = &up->port;
-	unsigned int flags;
-
-	console_atomic_lock(&flags);
-	if (atomic_read(&ier_counter) > 0)
-		atomic_set(&ier_value, ier);
-	else
-		serial_port_out(port, UART_IER, ier);
-	console_atomic_unlock(flags);
-}
-
-void clear_ier(struct uart_8250_port *up)
-{
-	struct uart_port *port = &up->port;
-	unsigned int ier_cleared = 0;
-	unsigned int flags;
-	unsigned int ier;
-
-	console_atomic_lock(&flags);
-	atomic_inc(&ier_counter);
-	ier = serial_port_in(port, UART_IER);
-	if (up->capabilities & UART_CAP_UUE)
-		ier_cleared = UART_IER_UUE;
-	if (ier != ier_cleared) {
-		serial_port_out(port, UART_IER, ier_cleared);
-		atomic_set(&ier_value, ier);
-	}
-	console_atomic_unlock(flags);
-}
-EXPORT_SYMBOL_GPL(clear_ier);
-
-void restore_ier(struct uart_8250_port *up)
-{
-	struct uart_port *port = &up->port;
-	unsigned int flags;
-
-	console_atomic_lock(&flags);
-	if (atomic_fetch_dec(&ier_counter) == 1)
-		serial_port_out(port, UART_IER, atomic_read(&ier_value));
-	console_atomic_unlock(flags);
-}
-EXPORT_SYMBOL_GPL(restore_ier);
-
 #ifdef CONFIG_CONSOLE_POLL
 /*
  * Console polling routines for writing and reading from the uart while
@@ -2070,10 +2022,11 @@ static int serial8250_get_poll_char(stru
 static void serial8250_put_poll_char(struct uart_port *port,
 			 unsigned char c)
 {
+	unsigned int ier;
 	struct uart_8250_port *up = up_to_u8250p(port);
 
 	serial8250_rpm_get(up);
-	clear_ier(up);
+	ier = serial8250_clear_IER(up);
 
 	wait_for_xmitr(up, BOTH_EMPTY);
 	/*
@@ -2086,7 +2039,7 @@ static void serial8250_put_poll_char(str
 	 *	and restore the IER
 	 */
 	wait_for_xmitr(up, BOTH_EMPTY);
-	restore_ier(up);
+	serial8250_set_IER(up, ier);
 	serial8250_rpm_put(up);
 }
 
@@ -2394,7 +2347,7 @@ void serial8250_do_shutdown(struct uart_
 	 */
 	spin_lock_irqsave(&port->lock, flags);
 	up->ier = 0;
-	set_ier(up, 0);
+	serial8250_set_IER(up, 0);
 	spin_unlock_irqrestore(&port->lock, flags);
 
 	synchronize_irq(port->irq);
@@ -2679,7 +2632,7 @@ serial8250_do_set_termios(struct uart_po
 	if (up->capabilities & UART_CAP_RTOIE)
 		up->ier |= UART_IER_RTOIE;
 
-	set_ier(up, up->ier);
+	serial8250_set_IER(up, up->ier);
 
 	if (up->capabilities & UART_CAP_EFR) {
 		unsigned char efr = 0;
@@ -3189,12 +3142,13 @@ void serial8250_console_write_atomic(str
 {
 	struct uart_port *port = &up->port;
 	unsigned int flags;
+	unsigned int ier;
 
 	console_atomic_lock(&flags);
 
 	touch_nmi_watchdog();
 
-	clear_ier(up);
+	ier = serial8250_clear_IER(up);
 
 	if (atomic_fetch_inc(&up->console_printing)) {
 		uart_console_write(port, "\n", 1,
@@ -3204,7 +3158,7 @@ void serial8250_console_write_atomic(str
 	atomic_dec(&up->console_printing);
 
 	wait_for_xmitr(up, BOTH_EMPTY);
-	restore_ier(up);
+	serial8250_set_IER(up, ier);
 
 	console_atomic_unlock(flags);
 }
@@ -3220,13 +3174,14 @@ void serial8250_console_write(struct uar
 {
 	struct uart_port *port = &up->port;
 	unsigned long flags;
+	unsigned int ier;
 
 	touch_nmi_watchdog();
 
 	serial8250_rpm_get(up);
 	spin_lock_irqsave(&port->lock, flags);
 
-	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))) {
@@ -3243,7 +3198,7 @@ void serial8250_console_write(struct uar
 	 *	and restore the IER
 	 */
 	wait_for_xmitr(up, BOTH_EMPTY);
-	restore_ier(up);
+	serial8250_set_IER(up, ier);
 
 	/*
 	 *	The receive handling will happen properly because the