[PATCH tty v1 37/74] serial: meson: Use port lock wrappers

[PATCH tty v1 37/74] serial: meson: Use port lock wrappers

[John Ogness]

From: Thomas Gleixner <tglx@linutronix.de>

When a serial port is used for kernel console output, then all
modifications to the UART registers which are done from other contexts,
e.g. getty, termios, are interference points for the kernel console.

So far this has been ignored and the printk output is based on the
principle of hope. The rework of the console infrastructure which aims to
support threaded and atomic consoles, requires to mark sections which
modify the UART registers as unsafe. This allows the atomic write function
to make informed decisions and eventually to restore operational state. It
also allows to prevent the regular UART code from modifying UART registers
while printk output is in progress.

All modifications of UART registers are guarded by the UART port lock,
which provides an obvious synchronization point with the console
infrastructure.

To avoid adding this functionality to all UART drivers, wrap the
spin_[un]lock*() invocations for uart_port::lock into helper functions
which just contain the spin_[un]lock*() invocations for now. In a
subsequent step these helpers will gain the console synchronization
mechanisms.

Converted with coccinelle. No functional change.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 drivers/tty/serial/meson_uart.c | 30 +++++++++++++++---------------
 1 file changed, 15 insertions(+), 15 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 790d910dafa5..45cc23e9e399 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -129,14 +129,14 @@ static void meson_uart_shutdown(struct uart_port *port)
 
 	free_irq(port->irq, port);
 
-	spin_lock_irqsave(&port->lock, flags);
+	uart_port_lock_irqsave(port, &flags);
 
 	val = readl(port->membase + AML_UART_CONTROL);
 	val &= ~AML_UART_RX_EN;
 	val &= ~(AML_UART_RX_INT_EN | AML_UART_TX_INT_EN);
 	writel(val, port->membase + AML_UART_CONTROL);
 
-	spin_unlock_irqrestore(&port->lock, flags);
+	uart_port_unlock_irqrestore(port, flags);
 }
 
 static void meson_uart_start_tx(struct uart_port *port)
@@ -238,7 +238,7 @@ static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)
 {
 	struct uart_port *port = (struct uart_port *)dev_id;
 
-	spin_lock(&port->lock);
+	uart_port_lock(port);
 
 	if (!(readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY))
 		meson_receive_chars(port);
@@ -248,7 +248,7 @@ static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)
 			meson_uart_start_tx(port);
 	}
 
-	spin_unlock(&port->lock);
+	uart_port_unlock(port);
 
 	return IRQ_HANDLED;
 }
@@ -284,7 +284,7 @@ static int meson_uart_startup(struct uart_port *port)
 	u32 val;
 	int ret = 0;
 
-	spin_lock_irqsave(&port->lock, flags);
+	uart_port_lock_irqsave(port, &flags);
 
 	val = readl(port->membase + AML_UART_CONTROL);
 	val |= AML_UART_CLEAR_ERR;
@@ -301,7 +301,7 @@ static int meson_uart_startup(struct uart_port *port)
 	val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2));
 	writel(val, port->membase + AML_UART_MISC);
 
-	spin_unlock_irqrestore(&port->lock, flags);
+	uart_port_unlock_irqrestore(port, flags);
 
 	ret = request_irq(port->irq, meson_uart_interrupt, 0,
 			  port->name, port);
@@ -341,7 +341,7 @@ static void meson_uart_set_termios(struct uart_port *port,
 	unsigned long flags;
 	u32 val;
 
-	spin_lock_irqsave(&port->lock, flags);
+	uart_port_lock_irqsave(port, &flags);
 
 	cflags = termios->c_cflag;
 	iflags = termios->c_iflag;
@@ -401,7 +401,7 @@ static void meson_uart_set_termios(struct uart_port *port,
 					    AML_UART_FRAME_ERR;
 
 	uart_update_timeout(port, termios->c_cflag, baud);
-	spin_unlock_irqrestore(&port->lock, flags);
+	uart_port_unlock_irqrestore(port, flags);
 }
 
 static int meson_uart_verify_port(struct uart_port *port,
@@ -460,14 +460,14 @@ static int meson_uart_poll_get_char(struct uart_port *port)
 	u32 c;
 	unsigned long flags;
 
-	spin_lock_irqsave(&port->lock, flags);
+	uart_port_lock_irqsave(port, &flags);
 
 	if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
 		c = NO_POLL_CHAR;
 	else
 		c = readl(port->membase + AML_UART_RFIFO);
 
-	spin_unlock_irqrestore(&port->lock, flags);
+	uart_port_unlock_irqrestore(port, flags);
 
 	return c;
 }
@@ -478,7 +478,7 @@ static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
 	u32 reg;
 	int ret;
 
-	spin_lock_irqsave(&port->lock, flags);
+	uart_port_lock_irqsave(port, &flags);
 
 	/* Wait until FIFO is empty or timeout */
 	ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg,
@@ -502,7 +502,7 @@ static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
 		dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n");
 
 out:
-	spin_unlock_irqrestore(&port->lock, flags);
+	uart_port_unlock_irqrestore(port, flags);
 }
 
 #endif /* CONFIG_CONSOLE_POLL */
@@ -559,9 +559,9 @@ static void meson_serial_port_write(struct uart_port *port, const char *s,
 	if (port->sysrq) {
 		locked = 0;
 	} else if (oops_in_progress) {
-		locked = spin_trylock(&port->lock);
+		locked = uart_port_trylock(port);
 	} else {
-		spin_lock(&port->lock);
+		uart_port_lock(port);
 		locked = 1;
 	}
 
@@ -573,7 +573,7 @@ static void meson_serial_port_write(struct uart_port *port, const char *s,
 	writel(val, port->membase + AML_UART_CONTROL);
 
 	if (locked)
-		spin_unlock(&port->lock);
+		uart_port_unlock(port);
 	local_irq_restore(flags);
 }
 
-- 
2.39.2


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Re: [PATCH tty v1 37/74] serial: meson: Use port lock wrappers

[Neil Armstrong]

On 14/09/2023 20:37, John Ogness wrote:
> From: Thomas Gleixner <tglx@linutronix.de>
> 
> When a serial port is used for kernel console output, then all
> modifications to the UART registers which are done from other contexts,
> e.g. getty, termios, are interference points for the kernel console.
> 
> So far this has been ignored and the printk output is based on the
> principle of hope. The rework of the console infrastructure which aims to
> support threaded and atomic consoles, requires to mark sections which
> modify the UART registers as unsafe. This allows the atomic write function
> to make informed decisions and eventually to restore operational state. It
> also allows to prevent the regular UART code from modifying UART registers
> while printk output is in progress.
> 
> All modifications of UART registers are guarded by the UART port lock,
> which provides an obvious synchronization point with the console
> infrastructure.
> 
> To avoid adding this functionality to all UART drivers, wrap the
> spin_[un]lock*() invocations for uart_port::lock into helper functions
> which just contain the spin_[un]lock*() invocations for now. In a
> subsequent step these helpers will gain the console synchronization
> mechanisms.
> 
> Converted with coccinelle. No functional change.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
>   drivers/tty/serial/meson_uart.c | 30 +++++++++++++++---------------
>   1 file changed, 15 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
> index 790d910dafa5..45cc23e9e399 100644
> --- a/drivers/tty/serial/meson_uart.c
> +++ b/drivers/tty/serial/meson_uart.c
> @@ -129,14 +129,14 @@ static void meson_uart_shutdown(struct uart_port *port)
>   
>   	free_irq(port->irq, port);
>   
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>   
>   	val = readl(port->membase + AML_UART_CONTROL);
>   	val &= ~AML_UART_RX_EN;
>   	val &= ~(AML_UART_RX_INT_EN | AML_UART_TX_INT_EN);
>   	writel(val, port->membase + AML_UART_CONTROL);
>   
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>   }
>   
>   static void meson_uart_start_tx(struct uart_port *port)
> @@ -238,7 +238,7 @@ static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)
>   {
>   	struct uart_port *port = (struct uart_port *)dev_id;
>   
> -	spin_lock(&port->lock);
> +	uart_port_lock(port);
>   
>   	if (!(readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY))
>   		meson_receive_chars(port);
> @@ -248,7 +248,7 @@ static irqreturn_t meson_uart_interrupt(int irq, void *dev_id)
>   			meson_uart_start_tx(port);
>   	}
>   
> -	spin_unlock(&port->lock);
> +	uart_port_unlock(port);
>   
>   	return IRQ_HANDLED;
>   }
> @@ -284,7 +284,7 @@ static int meson_uart_startup(struct uart_port *port)
>   	u32 val;
>   	int ret = 0;
>   
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>   
>   	val = readl(port->membase + AML_UART_CONTROL);
>   	val |= AML_UART_CLEAR_ERR;
> @@ -301,7 +301,7 @@ static int meson_uart_startup(struct uart_port *port)
>   	val = (AML_UART_RECV_IRQ(1) | AML_UART_XMIT_IRQ(port->fifosize / 2));
>   	writel(val, port->membase + AML_UART_MISC);
>   
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>   
>   	ret = request_irq(port->irq, meson_uart_interrupt, 0,
>   			  port->name, port);
> @@ -341,7 +341,7 @@ static void meson_uart_set_termios(struct uart_port *port,
>   	unsigned long flags;
>   	u32 val;
>   
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>   
>   	cflags = termios->c_cflag;
>   	iflags = termios->c_iflag;
> @@ -401,7 +401,7 @@ static void meson_uart_set_termios(struct uart_port *port,
>   					    AML_UART_FRAME_ERR;
>   
>   	uart_update_timeout(port, termios->c_cflag, baud);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>   }
>   
>   static int meson_uart_verify_port(struct uart_port *port,
> @@ -460,14 +460,14 @@ static int meson_uart_poll_get_char(struct uart_port *port)
>   	u32 c;
>   	unsigned long flags;
>   
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>   
>   	if (readl(port->membase + AML_UART_STATUS) & AML_UART_RX_EMPTY)
>   		c = NO_POLL_CHAR;
>   	else
>   		c = readl(port->membase + AML_UART_RFIFO);
>   
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>   
>   	return c;
>   }
> @@ -478,7 +478,7 @@ static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
>   	u32 reg;
>   	int ret;
>   
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>   
>   	/* Wait until FIFO is empty or timeout */
>   	ret = readl_poll_timeout_atomic(port->membase + AML_UART_STATUS, reg,
> @@ -502,7 +502,7 @@ static void meson_uart_poll_put_char(struct uart_port *port, unsigned char c)
>   		dev_err(port->dev, "Timeout waiting for UART TX EMPTY\n");
>   
>   out:
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>   }
>   
>   #endif /* CONFIG_CONSOLE_POLL */
> @@ -559,9 +559,9 @@ static void meson_serial_port_write(struct uart_port *port, const char *s,
>   	if (port->sysrq) {
>   		locked = 0;
>   	} else if (oops_in_progress) {
> -		locked = spin_trylock(&port->lock);
> +		locked = uart_port_trylock(port);
>   	} else {
> -		spin_lock(&port->lock);
> +		uart_port_lock(port);
>   		locked = 1;
>   	}
>   
> @@ -573,7 +573,7 @@ static void meson_serial_port_write(struct uart_port *port, const char *s,
>   	writel(val, port->membase + AML_UART_CONTROL);
>   
>   	if (locked)
> -		spin_unlock(&port->lock);
> +		uart_port_unlock(port);
>   	local_irq_restore(flags);
>   }
>   

Acked-by: Neil Armstrong <neil.armstrong@linaro.org>

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