serial: do not restore interrupt state in sysrq helper

The uart_unlock_and_check_sysrq() helper can be used to defer processing
of sysrq until the interrupt handler has released the port lock and is
about to return.

Since commit 81e2073c ("genirq: Disable interrupts for force
threaded handlers") interrupt handlers that are not explicitly requested
as threaded are always called with interrupts disabled and there is no
need to save the interrupt state when taking the port lock.

Instead of adding another sysrq helper for when the interrupt state has
not needlessly been saved, drop the state parameter from
uart_unlock_and_check_sysrq() and update its callers to no longer
explicitly disable interrupts in their interrupt handlers.

Cc: Joel Stanley <joel@jms.id.au>
Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20210416140557.25177-2-johan@kernel.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_aspeed_vuart.c

@@ -320,7 +320,6 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
 {
 	struct uart_8250_port *up = up_to_u8250p(port);
 	unsigned int iir, lsr;
-	unsigned long flags;
 	int space, count;
 
 	iir = serial_port_in(port, UART_IIR);
@@ -328,7 +327,7 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
 	if (iir & UART_IIR_NO_INT)
 		return 0;
 
-	spin_lock_irqsave(&port->lock, flags);
+	spin_lock(&port->lock);
 
 	lsr = serial_port_in(port, UART_LSR);
 
@@ -364,7 +363,7 @@ static int aspeed_vuart_handle_irq(struct uart_port *port)
 	if (lsr & UART_LSR_THRE)
 		serial8250_tx_chars(up);
 
-	uart_unlock_and_check_sysrq(port, flags);
+	uart_unlock_and_check_sysrq(port);
 
 	return 1;
 }

drivers/tty/serial/8250/8250_fsl.c

@@ -30,15 +30,14 @@ struct fsl8250_data {
 int fsl8250_handle_irq(struct uart_port *port)
 {
 	unsigned char lsr, orig_lsr;
-	unsigned long flags;
 	unsigned int iir;
 	struct uart_8250_port *up = up_to_u8250p(port);
 
-	spin_lock_irqsave(&up->port.lock, flags);
+	spin_lock(&up->port.lock);
 
 	iir = port->serial_in(port, UART_IIR);
 	if (iir & UART_IIR_NO_INT) {
-		spin_unlock_irqrestore(&up->port.lock, flags);
+		spin_unlock(&up->port.lock);
 		return 0;
 	}
 
@@ -46,7 +45,7 @@ int fsl8250_handle_irq(struct uart_port *port)
 	if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) {
 		up->lsr_saved_flags &= ~UART_LSR_BI;
 		port->serial_in(port, UART_RX);
-		spin_unlock_irqrestore(&up->port.lock, flags);
+		spin_unlock(&up->port.lock);
 		return 1;
 	}
 
@@ -82,7 +81,9 @@ int fsl8250_handle_irq(struct uart_port *port)
 		serial8250_tx_chars(up);
 
 	up->lsr_saved_flags = orig_lsr;
-	uart_unlock_and_check_sysrq(&up->port, flags);
+
+	uart_unlock_and_check_sysrq(&up->port);
+
 	return 1;
 }
 EXPORT_SYMBOL_GPL(fsl8250_handle_irq);

drivers/tty/serial/8250/8250_omap.c

@@ -1143,7 +1143,6 @@ static int omap_8250_dma_handle_irq(struct uart_port *port)
 	struct uart_8250_port *up = up_to_u8250p(port);
 	struct omap8250_priv *priv = up->port.private_data;
 	unsigned char status;
-	unsigned long flags;
 	u8 iir;
 
 	serial8250_rpm_get(up);
@@ -1154,7 +1153,7 @@ static int omap_8250_dma_handle_irq(struct uart_port *port)
 		return IRQ_HANDLED;
 	}
 
-	spin_lock_irqsave(&port->lock, flags);
+	spin_lock(&port->lock);
 
 	status = serial_port_in(port, UART_LSR);
 
@@ -1179,7 +1178,8 @@ static int omap_8250_dma_handle_irq(struct uart_port *port)
 		}
 	}
 
-	uart_unlock_and_check_sysrq(port, flags);
+	uart_unlock_and_check_sysrq(port);
+
 	serial8250_rpm_put(up);
 	return 1;
 }

drivers/tty/serial/8250/8250_port.c

@@ -1879,14 +1879,13 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 {
 	unsigned char status;
-	unsigned long flags;
 	struct uart_8250_port *up = up_to_u8250p(port);
 	bool skip_rx = false;
 
 	if (iir & UART_IIR_NO_INT)
 		return 0;
 
-	spin_lock_irqsave(&port->lock, flags);
+	spin_lock(&port->lock);
 
 	status = serial_port_in(port, UART_LSR);
 
@@ -1912,7 +1911,8 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir)
 		(up->ier & UART_IER_THRI))
 		serial8250_tx_chars(up);
 
-	uart_unlock_and_check_sysrq(port, flags);
+	uart_unlock_and_check_sysrq(port);
+
 	return 1;
 }
 EXPORT_SYMBOL_GPL(serial8250_handle_irq);

drivers/tty/serial/qcom_geni_serial.c

@@ -818,7 +818,6 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
 	u32 s_irq_status;
 	u32 geni_status;
 	struct uart_port *uport = dev;
-	unsigned long flags;
 	bool drop_rx = false;
 	struct tty_port *tport = &uport->state->port;
 	struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
@@ -826,7 +825,8 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
 	if (uport->suspended)
 		return IRQ_NONE;
 
-	spin_lock_irqsave(&uport->lock, flags);
+	spin_lock(&uport->lock);
+
 	m_irq_status = readl(uport->membase + SE_GENI_M_IRQ_STATUS);
 	s_irq_status = readl(uport->membase + SE_GENI_S_IRQ_STATUS);
 	geni_status = readl(uport->membase + SE_GENI_STATUS);
@@ -861,7 +861,7 @@ static irqreturn_t qcom_geni_serial_isr(int isr, void *dev)
 		qcom_geni_serial_handle_rx(uport, drop_rx);
 
 out_unlock:
-	uart_unlock_and_check_sysrq(uport, flags);
+	uart_unlock_and_check_sysrq(uport);
 
 	return IRQ_HANDLED;
 }

include/linux/serial_core.h

@@ -500,19 +500,19 @@ static inline int uart_prepare_sysrq_char(struct uart_port *port, unsigned int c
 	return 0;
 }
 
-static inline void uart_unlock_and_check_sysrq(struct uart_port *port, unsigned long irqflags)
+static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
 {
 	int sysrq_ch;
 
 	if (!port->has_sysrq) {
-		spin_unlock_irqrestore(&port->lock, irqflags);
+		spin_unlock(&port->lock);
 		return;
 	}
 
 	sysrq_ch = port->sysrq_ch;
 	port->sysrq_ch = 0;
 
-	spin_unlock_irqrestore(&port->lock, irqflags);
+	spin_unlock(&port->lock);
 
 	if (sysrq_ch)
 		handle_sysrq(sysrq_ch);
@@ -526,9 +526,9 @@ static inline int uart_prepare_sysrq_char(struct uart_port *port, unsigned int c
 {
 	return 0;
 }
-static inline void uart_unlock_and_check_sysrq(struct uart_port *port, unsigned long irqflags)
+static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
 {
-	spin_unlock_irqrestore(&port->lock, irqflags);
+	spin_unlock(&port->lock);
 }
 #endif	/* CONFIG_MAGIC_SYSRQ_SERIAL */