On Thu 2023-09-14 20:43:18, 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.
>
> 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@xxxxxxxxxxxxx>
> ---
> 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
> +/**
> + * 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);
> +}
IMHO, it would have been better to pass the flags variable directly
via a macro as it is done in most *_lock_*_irqsafe() APIs. I mean
something like:
/**
* uart_port_trylock_irqsave - Try to lock the UART port, save and disable interrupts
* @up: Pointer to UART port structure
* @flags: Interrupt flags storage
*
* Returns: True if lock was acquired, false otherwise
*/
#define uart_port_lock_irqsave(up, flags) \
({ \
local_irq_save(flags); \
uart_port_lock(lock) \
})
> +
> +/**
> + * 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);
> +}
Similar here:
/**
* uart_port_trylock_irqsave - Try to lock the UART port, save and disable interrupts
* @up: Pointer to UART port structure
* @flags: Interrupt flags storage
*
* Returns: True if lock was acquired, false otherwise
*/
#define uart_port_trylock_irqsave(up, flags) \
({ \
bool __ret; \
\
local_irq_save(flags); \
__ret = uart_port_trylock(lock) \
if (!__ret) \
local_irq_restore(flags); \
__ret; \
})
I do not resist on this rather cosmetic change. The current code seems
to be doing what is expected. Feel free to keep it and use:
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Best Regards,
Petr
PS: I am sorry for the late review. I have made a quick look on Monday
and it looked straightforward. I have got this idea today when
having a closer look.
