diff mbox series

[tty,v1,08/74] serial: 8250_dw: Use port lock wrappers

Message ID 20230914183831.587273-9-john.ogness@linutronix.de
State New
Headers
Series serial: wrappers for uart port lock |

Commit Message

John Ogness Sept. 14, 2023, 6:37 p.m. UTC 
  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/8250/8250_dw.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Comments

Ilpo Järvinen Sept. 15, 2023, 9:16 a.m. UTC | #1 
On Thu, 14 Sep 2023, 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/8250/8250_dw.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index f4cafca1a7da..95d45dce0880 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -263,20 +263,20 @@ static int dw8250_handle_irq(struct uart_port *p)
>  	 * so we limit the workaround only to non-DMA mode.
>  	 */
>  	if (!up->dma && rx_timeout) {
> -		spin_lock_irqsave(&p->lock, flags);
> +		uart_port_lock_irqsave(p, &flags);
>  		status = serial_lsr_in(up);
>  
>  		if (!(status & (UART_LSR_DR | UART_LSR_BI)))
>  			(void) p->serial_in(p, UART_RX);
>  
> -		spin_unlock_irqrestore(&p->lock, flags);
> +		uart_port_unlock_irqrestore(p, flags);
>  	}
>  
>  	/* Manually stop the Rx DMA transfer when acting as flow controller */
>  	if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
> -		spin_lock_irqsave(&p->lock, flags);
> +		uart_port_lock_irqsave(p, &flags);
>  		status = serial_lsr_in(up);
> -		spin_unlock_irqrestore(&p->lock, flags);
> +		uart_port_unlock_irqrestore(p, flags);
>  
>  		if (status & (UART_LSR_DR | UART_LSR_BI)) {
>  			dw8250_writel_ext(p, RZN1_UART_RDMACR, 0);
> 

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
diff mbox series

Patch

diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
index f4cafca1a7da..95d45dce0880 100644
--- a/drivers/tty/serial/8250/8250_dw.c
+++ b/drivers/tty/serial/8250/8250_dw.c
@@ -263,20 +263,20 @@  static int dw8250_handle_irq(struct uart_port *p)
 	 * so we limit the workaround only to non-DMA mode.
 	 */
 	if (!up->dma && rx_timeout) {
-		spin_lock_irqsave(&p->lock, flags);
+		uart_port_lock_irqsave(p, &flags);
 		status = serial_lsr_in(up);
 
 		if (!(status & (UART_LSR_DR | UART_LSR_BI)))
 			(void) p->serial_in(p, UART_RX);
 
-		spin_unlock_irqrestore(&p->lock, flags);
+		uart_port_unlock_irqrestore(p, flags);
 	}
 
 	/* Manually stop the Rx DMA transfer when acting as flow controller */
 	if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
-		spin_lock_irqsave(&p->lock, flags);
+		uart_port_lock_irqsave(p, &flags);
 		status = serial_lsr_in(up);
-		spin_unlock_irqrestore(&p->lock, flags);
+		uart_port_unlock_irqrestore(p, flags);
 
 		if (status & (UART_LSR_DR | UART_LSR_BI)) {
 			dw8250_writel_ext(p, RZN1_UART_RDMACR, 0);