Re: [PATCH v11 4/8] serial: 8250_omap: quiesce DMA IRQ handling before shutdown

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] serial: 8250_omap: UART_OMAP_EFR2 cleared before locked RX
  DMA flush
--

commit 4f01158f98251ff9fc53053baff46ab365f1866d
Author: James Hilliard <james.hilliard1@gmail.com>

serial: 8250_omap: quiesce DMA IRQ handling before shutdown

This commit gates DMA IRQ handling on up->dma->shutting_down under the
port lock, moves the final RX DMA flush into that locked section, and
switches omap_8250_shutdown() from disable_irq_nosync() to disable_irq()
before releasing DMA resources.

> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 5e114dd8f9bfb..51013dd2d8510 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -771,10 +771,6 @@ static void omap_8250_shutdown(struct uart_port *port)
>  	guard(serial8250_rpm)(up);
>  
>  	flush_work(&priv->qos_work);
> -	if (up->dma) {
> -		guard(uart_port_lock_irq)(port);
> -		omap_8250_rx_dma_flush(up);
> -	}
>  
>  	serial_out(up, UART_OMAP_WER, 0);
>  	if (priv->habit & UART_HAS_EFR2)
> @@ -782,13 +778,16 @@ static void omap_8250_shutdown(struct uart_port *port)
>  
>  	/* Synchronize UART_IER access against the console. */
>  	scoped_guard(uart_port_lock_irq, port) {
> -		if (up->dma)
> +		if (up->dma) {
>  			up->dma->shutting_down = true;
> +			omap_8250_rx_dma_flush(up);
> +		}
>  		up->ier = 0;
>  		serial_out(up, UART_IER, 0);
>  	}

[Severity: Medium]
Can clearing UART_OMAP_EFR2 before acquiring port->lock leave
UART_OMAP_EFR2_TIMEOUT_BEHAVE set after shutdown?

Moving omap_8250_rx_dma_flush() into the locked block places it after
serial_out(up, UART_OMAP_EFR2, 0x0):

CPU0                              CPU1
omap_8250_shutdown()              omap_8250_dma_handle_irq()
  serial_out(up, UART_OMAP_EFR2, 0x0)
                                    uart_port_lock(port)
                                    /* shutting_down is still false */
                                    am654_8250_handle_rx_dma()
                                      omap_8250_rx_dma(up)
                                      serial_out(up, UART_OMAP_EFR2,
                                        UART_OMAP_EFR2_TIMEOUT_BEHAVE)
                                    uart_port_unlock(port)
  uart_port_lock_irq(port)
  up->dma->shutting_down = true
  omap_8250_rx_dma_flush(up)      <-- EFR2 is not cleared again

Neither omap_8250_startup() nor omap8250_restore_regs() resets
UART_OMAP_EFR2, so UART_OMAP_EFR2_TIMEOUT_BEHAVE stays set across
shutdown.  Clearing UART_OMAP_EFR2 inside the port->lock block after
omap_8250_rx_dma_flush() would also match the flush-then-clear order in
am654_8250_handle_rx_dma().

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261109-submit-serial-8250-dma-cancel-v1-v11-0-6364edca63d6@gmail.com?part=4