linux-kernel - Re: [PATCH] tty: Remove pointless synchronize_irq() in uart_port

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Date:   Wed, 11 May 2022 08:21:36 +0200
From:   Jiri Slaby <jirislaby@...nel.org>
To:     Thomas Pfaff <tpfaff@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: Remove pointless synchronize_irq() in
 uart_port_shutdown()

On 10. 05. 22, 15:54, Thomas Pfaff wrote:
> From: Thomas Pfaff <tpfaff@....com>
> 
> Calling synchronize_irq() after free_irq() is pointless, the context to
> the irq is already lost.
> It was noticed while creating the bugfix "genirq: Synchronize interrupt
> thread startup".

That's correct for most drivers. But some drivers don't call free_irq() 
in ->shutdown(). So you likely have to move the synchronization to them. 
By a quick grep, I found icom, jsm, sccnxp, sifive, sunhv, and sunzilog.

> Signed-off-by: Thomas Pfaff <tpfaff@....com>
> ---
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 57840cf90388..b76e76e650ba 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1704,12 +1704,6 @@ static void uart_port_shutdown(struct tty_port *port)
>   	 */
>   	if (uport)
>   		uport->ops->shutdown(uport);
> -
> -	/*
> -	 * Ensure that the IRQ handler isn't running on another CPU.
> -	 */
> -	if (uport)
> -		synchronize_irq(uport->irq);
>   }
>   
>   static int uart_carrier_raised(struct tty_port *port)
> 
> 


-- 
js
suse labs