Re: [PATCH v9 2/8] serial: serialize asynchronous write wakeups with the port lock

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, Nov 02, 2026 at 04:14:29PM -0700, James Hilliard wrote:
> uart_write_wakeup() expects the UART port lock to be held. Several worker,
> DMA completion and interrupt paths call it without that lock, including
> indirect calls from uart_handle_cts_change() and the transmit helpers.
> 
> Take the port lock around these notifications or their transmit helper.
> Keep sleeping SPI and regmap accesses outside the locked region, and keep
> the FSL LPUART completion lock held through its wakeup. Acquire the port
> lock after releasing private channel locks to preserve the ordering used
> by UART callbacks. In the MUX timer, publish available FIFO space under
> the port lock and keep the hardware FIFO-drain wait outside it.
> 
> Use plain port locking in hard-IRQ handlers and in helpers whose callers
> already mask interrupts. Atmel status handling is also called during
> resume, where lock_suspended is acquired with interrupts disabled; JSM
> interrupt processing holds its IRQ-saving board lock. Keep IRQ-saving
> locking in workers, tasklets and other mixed-context paths.
> 
> Take the port lock after requesting the ST ASC interrupt and hold it
> through startup's transmit servicing and RX interrupt enable. The transmit
> helper can notify writers even when the FIFO is empty, and serial core
> calls startup without holding the port spinlock.
> 
> Use IRQ-safe locking in the Atmel RX and TX tasklets and SB1250 termios
> path, since their interrupt handlers now acquire the same port lock.
> Preserve the caller's interrupt state when releasing those locks.
> 
> On SB1250, lock modem-state updates after reading and filtering the change
> status, and wake modem-status waiters after unlocking. Take the TX lock
> inside its service routine so RX-only interrupts need no acquisition.
> Keep that lock across x_char handling, FIFO consumption and the decision
> to mask TX interrupts: a writer must not enqueue data and enable TX between
> the empty-FIFO check and the interrupt-mask write. Each TX invocation sends
> at most one character.
> 
> Serialize CLPS711x TX servicing and its interrupt-enable state with the
> port lock. Disable TX interrupts without waiting in stop_tx(), since a
> threaded handler may need that same lock. Have an already queued handler
> leave stopped output untouched, and drain it outside the lock during
> shutdown before the transmit FIFO can be released.
> 
> SCCNXP handles interrupts under a controller lock which its UART callbacks
> acquire with the port lock already held. Collect the ports needing wakeups
> in an unsigned long bitmap while servicing the controller, then release
> that lock before visiting the set bits, taking each port lock and
> rechecking the wakeup threshold. Removal drains the IRQ or timer before
> unregistering the ports.
> 
> This serializes write notifications with port-locked serial-core state
> changes, allowing readiness and transmit-storage reservations to gate the
> notification without a check-versus-shutdown race.
> 
> Cover DZ TX servicing and JSM Classic modem notifications as well. On
> DECstation ZS, acquire the port lock before the SCC lock and notify writers
> after releasing the SCC lock. Defer normal TX restart after console output
> to a worker, since console output can already run under the port lock.
> Check transmitter readiness before consuming another character and drain
> the restart worker during shutdown and removal. Release Lantiq's hardware
> lock through the transmit helper's completion hook before notifying the
> line discipline.

...

> +++ b/drivers/tty/serial/sccnxp.c
> @@ -10,6 +10,7 @@
>  #include <linux/clk.h>
>  #include <linux/delay.h>
>  #include <linux/err.h>
> +#include <linux/find.h>

Try to understand what AI is trying to achieve and why it compiles.
The above is wrong.

>  #include <linux/module.h>
>  #include <linux/device.h>
>  #include <linux/console.h>

...

> +static unsigned long sccnxp_handle_events(struct sccnxp_port *s)
>  {

> -	int i;
> +	unsigned int i;

This change seems unrelated to the patch. Again, slow down and READ what AI
produces before sending, please!

>  	u8 isr;

-- 
With Best Regards,
Andy Shevchenko