linux-kernel - Re: [PATCH tty v1 01/74] serial: core: Provide port lock wrappers

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Date:   Fri, 15 Sep 2023 12:25:57 +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>
Subject: Re: [PATCH tty v1 01/74] serial: core: Provide 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.
> 
> Provide wrapper functions for spin_[un]lock*(port->lock) invocations so
> that the console mechanics can be applied later on at a single place and
> does not require to copy the same logic all over the drivers.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/serial_core.h | 79 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 79 insertions(+)
> 
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index bb6f073bc159..f1d5c0d1568c 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -588,6 +588,85 @@ struct uart_port {
>  	void			*private_data;		/* generic platform data pointer */
>  };
>  
> +/**
> + * uart_port_lock - Lock the UART port
> + * @up:		Pointer to UART port structure
> + */
> +static inline void uart_port_lock(struct uart_port *up)
> +{
> +	spin_lock(&up->lock);
> +}
> +
> +/**
> + * uart_port_lock_irq - Lock the UART port and disable interrupts
> + * @up:		Pointer to UART port structure
> + */
> +static inline void uart_port_lock_irq(struct uart_port *up)
> +{
> +	spin_lock_irq(&up->lock);
> +}
> +
> +/**
> + * uart_port_lock_irqsave - Lock the UART port, save and disable interrupts
> + * @up:		Pointer to UART port structure
> + * @flags:	Pointer to interrupt flags storage
> + */
> +static inline void uart_port_lock_irqsave(struct uart_port *up, unsigned long *flags)
> +{
> +	spin_lock_irqsave(&up->lock, *flags);
> +}
> +
> +/**
> + * uart_port_trylock - Try to lock the UART port
> + * @up:		Pointer to UART port structure
> + *
> + * Returns: True if lock was acquired, false otherwise
> + */
> +static inline bool uart_port_trylock(struct uart_port *up)
> +{
> +	return spin_trylock(&up->lock);
> +}
> +
> +/**
> + * uart_port_trylock_irqsave - Try to lock the UART port, save and disable interrupts
> + * @up:		Pointer to UART port structure
> + * @flags:	Pointer to interrupt flags storage
> + *
> + * Returns: True if lock was acquired, false otherwise
> + */
> +static inline bool uart_port_trylock_irqsave(struct uart_port *up, unsigned long *flags)
> +{
> +	return spin_trylock_irqsave(&up->lock, *flags);
> +}
> +
> +/**
> + * uart_port_unlock - Unlock the UART port
> + * @up:		Pointer to UART port structure
> + */
> +static inline void uart_port_unlock(struct uart_port *up)
> +{
> +	spin_unlock(&up->lock);
> +}
> +
> +/**
> + * uart_port_unlock_irq - Unlock the UART port and re-enable interrupts
> + * @up:		Pointer to UART port structure
> + */
> +static inline void uart_port_unlock_irq(struct uart_port *up)
> +{
> +	spin_unlock_irq(&up->lock);
> +}
> +
> +/**
> + * uart_port_lock_irqrestore - Unlock the UART port, restore interrupts
> + * @up:		Pointer to UART port structure
> + * @flags:	The saved interrupt flags for restore
> + */
> +static inline void uart_port_unlock_irqrestore(struct uart_port *up, unsigned long flags)
> +{
> +	spin_unlock_irqrestore(&up->lock, flags);
> +}
> +
>  static inline int serial_port_in(struct uart_port *up, int offset)
>  {
>  	return up->serial_in(up, offset);
> 

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

-- 
 i.