linux-kernel - Re: [PATCH tty v1 07/74] serial: 8250

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Message-ID: <2410ffe1-d89c-8598-3e41-8ba2454088d@linux.intel.com>
Date:   Fri, 15 Sep 2023 12:14:52 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     John Ogness <john.ogness@...utronix.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH tty v1 07/74] serial: 8250_dma: Use port lock wrappers

On Thu, 14 Sep 2023, 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/8250/8250_dma.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
> index 7fa66501792d..8b30ca8fdd3f 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -22,7 +22,7 @@ static void __dma_tx_complete(void *param)
>  	dma_sync_single_for_cpu(dma->txchan->device->dev, dma->tx_addr,
>  				UART_XMIT_SIZE, DMA_TO_DEVICE);
>  
> -	spin_lock_irqsave(&p->port.lock, flags);
> +	uart_port_lock_irqsave(&p->port, &flags);
>  
>  	dma->tx_running = 0;
>  
> @@ -35,7 +35,7 @@ static void __dma_tx_complete(void *param)
>  	if (ret || !dma->tx_running)
>  		serial8250_set_THRI(p);
>  
> -	spin_unlock_irqrestore(&p->port.lock, flags);
> +	uart_port_unlock_irqrestore(&p->port, flags);
>  }
>  
>  static void __dma_rx_complete(struct uart_8250_port *p)
> @@ -70,7 +70,7 @@ static void dma_rx_complete(void *param)
>  	struct uart_8250_dma *dma = p->dma;
>  	unsigned long flags;
>  
> -	spin_lock_irqsave(&p->port.lock, flags);
> +	uart_port_lock_irqsave(&p->port, &flags);
>  	if (dma->rx_running)
>  		__dma_rx_complete(p);
>  
> @@ -80,7 +80,7 @@ static void dma_rx_complete(void *param)
>  	 */
>  	if (!dma->rx_running && (serial_lsr_in(p) & UART_LSR_DR))
>  		p->dma->rx_dma(p);
> -	spin_unlock_irqrestore(&p->port.lock, flags);
> +	uart_port_unlock_irqrestore(&p->port, flags);
>  }
>  
>  int serial8250_tx_dma(struct uart_8250_port *p)

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.