linux-kernel - Re: [PATCH tty v1 32/74] serial: liteuart: Use port lock wrappers

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Date:   Fri, 15 Sep 2023 09:40:47 -0400
From:   "Gabriel L. Somlo" <gsomlo@...il.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        Joel Stanley <joel@....id.au>
Subject: Re: [PATCH tty v1 32/74] serial: liteuart: Use port lock wrappers

Thanks!

Acked-by: Gabriel Somlo <gsomlo@...il.com>

On Thu, Sep 14, 2023 at 08:43:49PM +0206, John Ogness wrote:
> From: Thomas Gleixner <tglx@...utronix.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@...utronix.de>
> ---
>  drivers/tty/serial/liteuart.c | 20 ++++++++++----------
>  1 file changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/tty/serial/liteuart.c b/drivers/tty/serial/liteuart.c
> index d881cdd2a58f..a25ab1efe38f 100644
> --- a/drivers/tty/serial/liteuart.c
> +++ b/drivers/tty/serial/liteuart.c
> @@ -139,13 +139,13 @@ static irqreturn_t liteuart_interrupt(int irq, void *data)
>  	 * if polling, the context would be "in_serving_softirq", so use
>  	 * irq[save|restore] spin_lock variants to cover all possibilities
>  	 */
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>  	isr = litex_read8(port->membase + OFF_EV_PENDING) & uart->irq_reg;
>  	if (isr & EV_RX)
>  		liteuart_rx_chars(port);
>  	if (isr & EV_TX)
>  		liteuart_tx_chars(port);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  
>  	return IRQ_RETVAL(isr);
>  }
> @@ -195,10 +195,10 @@ static int liteuart_startup(struct uart_port *port)
>  		}
>  	}
>  
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>  	/* only enabling rx irqs during startup */
>  	liteuart_update_irq_reg(port, true, EV_RX);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  
>  	if (!port->irq) {
>  		timer_setup(&uart->timer, liteuart_timer, 0);
> @@ -213,9 +213,9 @@ static void liteuart_shutdown(struct uart_port *port)
>  	struct liteuart_port *uart = to_liteuart_port(port);
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>  	liteuart_update_irq_reg(port, false, EV_RX | EV_TX);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  
>  	if (port->irq)
>  		free_irq(port->irq, port);
> @@ -229,13 +229,13 @@ static void liteuart_set_termios(struct uart_port *port, struct ktermios *new,
>  	unsigned int baud;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>  
>  	/* update baudrate */
>  	baud = uart_get_baud_rate(port, new, old, 0, 460800);
>  	uart_update_timeout(port, new->c_cflag, baud);
>  
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  }
>  
>  static const char *liteuart_type(struct uart_port *port)
> @@ -382,9 +382,9 @@ static void liteuart_console_write(struct console *co, const char *s,
>  	uart = (struct liteuart_port *)xa_load(&liteuart_array, co->index);
>  	port = &uart->port;
>  
> -	spin_lock_irqsave(&port->lock, flags);
> +	uart_port_lock_irqsave(port, &flags);
>  	uart_console_write(port, s, count, liteuart_putchar);
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  }
>  
>  static int liteuart_console_setup(struct console *co, char *options)
> -- 
> 2.39.2
>