Subject: Re: local_irq_save not masking interrupts

From: Alex Zeffertt <[email-masked]>
Date: Tue, 26 Sep 2006 17:17:26 +0100

Hi Scott,

Thanks for your reply.  Comments below.

Scott Wood wrote:
> Alex Zeffertt wrote:
>> Well, mpc832xemds_phy_interrupt_enable() does nothing except call
>> request_irq(,,SA_SHIRQ,,).  I suspect that request_irq() is somehow
>> reenabling interrupts, but I can't see where it might be doing so.
> 
> One possibile way (in 2.6.18; I'm assuming 2.6.11 is similar) is that 
> request_irq() calls setup_irq(), which calls register_irq_proc() and 
> register_handler_proc(), both of which call proc_mkdir(), which 
> eventually calls proc_create(), which calls kmalloc() with GFP_KERNEL. 
> This is probably a bug, since request_irq itself uses GFP_ATOMIC, 
> indicating an intent for request_irq() to be safely callable in atomic 
> context.
> 

I agree this indicates an intent to make it atomic, but I don't see how
this could cause interrupts to become re-enabled during the request_irq()
call.  Also, since I am calling request_irq at insmod time, i.e. in process
context, both GFP_ flags *should* work.

> Can you disable the interrupts at the device level until the handler is 
> in place, and thus avoid the need to disable IRQs at all?
> 
> -Scott

Yup, I've come to the same conclusion.  I now, for each shared interrupt:

* initialise all the devices which share the interrupt, turning interrupt generation off

* register all handlers for each device which shares the interrupt

* turn interrupt generation back on for each device.

This avoids the original problem, but it does not explain it.  I still
can't see how I can get an interrupt on line 3 below:

1.         local_irq_save(flags);
2.         request_irq(MPC83xx_IRQ_EXT6, handler, SA_SHIRQ, "name", dev1);
3.
4.         request_irq(MPC83xx_IRQ_EXT6, handler, SA_SHIRQ, "name", dev2);
5          local_irq_restore(flags);

Regards,

Alex