On Thu, 14 Sep 2023, John Ogness wrote:
> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxx>
> ---
> include/linux/serial_core.h | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index f1d5c0d1568c..3091c62ec37b 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -1035,14 +1035,14 @@ static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
> u8 sysrq_ch;
>
> if (!port->has_sysrq) {
> - spin_unlock(&port->lock);
> + uart_port_unlock(port);
> return;
> }
>
> sysrq_ch = port->sysrq_ch;
> port->sysrq_ch = 0;
>
> - spin_unlock(&port->lock);
> + uart_port_unlock(port);
>
> if (sysrq_ch)
> handle_sysrq(sysrq_ch);
> @@ -1054,14 +1054,14 @@ static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port
> u8 sysrq_ch;
>
> if (!port->has_sysrq) {
> - spin_unlock_irqrestore(&port->lock, flags);
> + uart_port_unlock_irqrestore(port, flags);
> return;
> }
>
> sysrq_ch = port->sysrq_ch;
> port->sysrq_ch = 0;
>
> - spin_unlock_irqrestore(&port->lock, flags);
> + uart_port_unlock_irqrestore(port, flags);
>
> if (sysrq_ch)
> handle_sysrq(sysrq_ch);
> @@ -1077,12 +1077,12 @@ static inline int uart_prepare_sysrq_char(struct uart_port *port, u8 ch)
> }
> static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
> {
> - spin_unlock(&port->lock);
> + uart_port_unlock(port);
> }
> static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port,
> unsigned long flags)
> {
> - spin_unlock_irqrestore(&port->lock, flags);
> + uart_port_unlock_irqrestore(port, flags);
> }
> #endif /* CONFIG_MAGIC_SYSRQ_SERIAL */
>
>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
--
i.
