linux-kernel - Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request

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Date:	Thu, 10 Dec 2015 13:41:06 -0800
From:	Peter Hurley <peter@...leysoftware.com>
To:	Soren Brinkmann <soren.brinkmann@...inx.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.com>,
	Michal Simek <michal.simek@...inx.com>,
	linux-serial@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Moritz Fischer <moritz.fischer@...us.com>
Subject: Re: [PATCH LINUX v4 06/13] tty: xuartps: Move request_irq to after
 setting up the HW

On 12/05/2015 08:39 PM, Soren Brinkmann wrote:
> Request_irq() should be _after_ h/w programming, otherwise an
> interrupt could be triggered and in-progress before the h/w has been
> setup.

Slight misunderstanding. My fault; I should have been more explicit.

1. Any setup necessary for the isr not to be confused and misdirect spurious
   interrupts (or hang) should be before installing the isr with request_irq()
   None of this code should trigger an interrupt.
2. Clear pending interrupts
3. Install the isr with request_irq()
4. Enable interrupts

For extra safety, first disable interrupts before starting h/w programming.

I would do the v5 series in the same order as the v3 series only up to
what I reviewed. Then do another series with the remainder plus new changes, ok?

Regards,
Peter Hurley

> Reported-by: Peter Hurley <peter@...leysoftware.com>
> Signed-off-by: Soren Brinkmann <soren.brinkmann@...inx.com>
> ---
> v4:
>  - this patch has been added. Thanks to Peter for pointing it out and providing
>    commit message
> ---
>  drivers/tty/serial/xilinx_uartps.c | 9 ++-------
>  1 file changed, 2 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index 6ffd3bbe3e18..1e9053656610 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -759,12 +759,7 @@ static void cdns_uart_set_termios(struct uart_port *port,
>  static int cdns_uart_startup(struct uart_port *port)
>  {
>  	unsigned long flags;
> -	unsigned int retval = 0, status = 0;
> -
> -	retval = request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME,
> -								(void *)port);
> -	if (retval)
> -		return retval;
> +	unsigned int status = 0;
>  
>  	spin_lock_irqsave(&port->lock, flags);
>  
> @@ -818,7 +813,7 @@ static int cdns_uart_startup(struct uart_port *port)
>  
>  	spin_unlock_irqrestore(&port->lock, flags);
>  
> -	return retval;
> +	return request_irq(port->irq, cdns_uart_isr, 0, CDNS_UART_NAME, port);
>  }
>  
>  /**
> 

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