linux-kernel - Re: 2.6.31-rt11 freeze on userland start on ARM

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Date:	Wed, 30 Sep 2009 14:57:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Remy Bohmer <linux@...mer.net>
cc:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.31-rt11 freeze on userland start on ARM

On Mon, 21 Sep 2009, Remy Bohmer wrote:
> So, as workaround/test I made this change:
> 
> Index: linux-2.6.31/drivers/serial/atmel_serial.c
> ===================================================================
> --- linux-2.6.31.orig/drivers/serial/atmel_serial.c	2009-09-21
> 19:44:48.000000000 +0200
> +++ linux-2.6.31/drivers/serial/atmel_serial.c	2009-09-21
> 19:45:15.000000000 +0200
> @@ -808,7 +808,8 @@ static int atmel_startup(struct uart_por
>  	/*
>  	 * Allocate the IRQ
>  	 */
> -	retval = request_irq(port->irq, atmel_interrupt, IRQF_SHARED,
> +	retval = request_irq(port->irq, atmel_interrupt,
> +			IRQF_SHARED | IRQF_NODELAY,
>  			tty ? tty->name : "atmel_serial", port);
>  	if (retval) {
>  		printk("atmel_serial: atmel_startup - Can't get irq\n");

The serial irq cannot run in hard irq context.

There are two solutions to this problem:

1) Use the other timer which is available on AT91.

2) Make the serial driver explicitely threaded and check in the
hardirq handler whether the irq originated from the serial driver. If
yes, disable it in the serial device and return IRQ_WAKE_THREAD
otherwise return IRQ_NONE.

Thanks,

	tglx
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