linux-kernel - Re: [PATCH] amba-pl011: clear previous interrupts before request

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Date:	Wed, 18 Jan 2012 10:15:55 +0000
From:	Russell King <rmk@....linux.org.uk>
To:	Shreshtha Kumar SAHU <shreshthakumar.sahu@...ricsson.com>
Cc:	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] amba-pl011: clear previous interrupts before
	request_irq

On Wed, Jan 18, 2012 at 03:34:11PM +0530, Shreshtha Kumar SAHU wrote:
> 
> >From 0742fc49405b2a6f562981f61d93198e1595f30d Mon Sep 17 00:00:00 2001
> From: Shreshtha Kumar Sahu <shreshthakumar.sahu@...ricsson.com>
> Date: Tue, 17 Jan 2012 12:23:19 +0530
> Subject: [PATCH v2] amba-pl011: clear previous interrupts before request_irq
> 
> All previous interrupts should be cleared before installing
> interrupt handler i.e. before request_irq. pl011_shutdown
> clears the interrupt register but there may be case where
> bootloader transfers control to kernel and there are some
> pending interrupts. In this case interrupt handler will get
> called even before interrupt mask is enabled.
> 
> Acked-by: Linus Walleij <linus.walleij@...aro.org>

No sign-off, and I don't understand the problem being aluded to in the
description above - particularly the last sentence.

In theory, we should be prepared for the interrupt handler to be called
immediately after request_irq() returns, and not have the driver misbehave
because of that.  Maybe a better solution would be to move request_irq()
a bit later?

But first, having a clearer description of the problem you're seeing
would be beneficial.

> ---
>  drivers/tty/serial/amba-pl011.c |    9 +++++++++
>  1 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 6958594..6dafaa2 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -1381,6 +1381,15 @@ static int pl011_startup(struct uart_port *port)
>  	uap->port.uartclk = clk_get_rate(uap->clk);
>  
>  	/*
> +	 * Clear previous interrupts before installing interrupt handler
> +	 */
> +	spin_lock_irq(&uap->port.lock);
> +	uap->im = 0;
> +	writew(uap->im, uap->port.membase + UART011_IMSC);
> +	writew(0xffff, uap->port.membase + UART011_ICR);
> +	spin_unlock_irq(&uap->port.lock);
> +
> +	/*
>  	 * Allocate the IRQ
>  	 */
>  	retval = request_irq(uap->port.irq, pl011_int, 0, "uart-pl011", uap);
> -- 
> 1.7.4.3
> 

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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