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>
> ---
> 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@xxxxxxxxxxxxxxx>
--
i.
