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Re: Preempted interrupt handler

To: Yoann Allain <yallain@avilinks.com>
Subject: Re: Preempted interrupt handler
From: Ralf Baechle <ralf@linux-mips.org>
Date: Tue, 20 Dec 2005 14:18:29 +0100
Cc: "'linux-mips@linux-mips.org'" <linux-mips@linux-mips.org>
In-reply-to: <43A6F155.7080402@avilinks.com>
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On Mon, Dec 19, 2005 at 06:43:49PM +0100, Yoann Allain wrote:

> I'm actually working on a driver for a Marvell chip on a MIPS-based 
> board running a 2.4 kernel. I have one problem:
> In my module, my interrupt handler is never executed. I have traced the 
> code until action->handler(irq, action->dev_id, regs)  in 
> handle_IRQ_event() but when the handler should be executed, it is not 
> and the kernel reenters in the low-level interrupt dispatch routine 
> (because we're using level sensitive interrupts and it is still up). 
> I've checked that the function pointer called is the one of my handler 
> but my routine is never entered.
> 
> But when my handler is included in the kernel (ie not compiled as a 
> module), it works! My function gets executed and acks the interrupt. In 
> this case all goes fine.
>
> Moreover, I've noticed that the kernel symbols are mapped at adresses 
> like 0x80258040 (start_kernel) but my module (and so is my handler) is 
> loaded at something like 0xc000275c . I was thinking the module would be 
> loaded in the same memory area as the kernel, so I think this is weird...
> Perhaps, the module handler can't be executed because of its location 
> but I don't know how to fix this.

Good new then - you don't need to fix anything :-)

The sympthoms you're describing are not specific enough, so only some
general advice:

 - Make sure you're running a current version of modutils; older versions
   have a number of bugs that could result in almost any kind of ill
   behaviour.
 - Make sure all object files of the modules have been built with
   -mlong-calls.  That's done automatically by the kernel's makefiles
   but not necessarily when building out of tree and certain versions
   would silently tolerate the resulting relocation error.

  Ralf

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