Use of IRQF_DISABLED along with IRQF_SHARED

Hi,

This is regarding the following code in kernel/irq/handle.c. Consider the case of a shared IRQ line, where two handlers are registered such that first handler does not specify IRQF_DISABLED, but the second one does. But it seems both the handlers will be called IRQs ENABLED (which is certainly not what the second handler expects).

I also checked but could not find anything that stops me from registering two shared ISRs - one with IRQF_DISABLED & another without this flag. Am I missing something here?

irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction *action)
{
irqreturn_t ret, retval = IRQ_NONE;
unsigned int status = 0;

handle_dynamic_tick(action);

if (!(action->flags & IRQF_DISABLED))
local_irq_enable_in_hardirq();

do {
ret = action->handler(irq, action->dev_id);
if (ret == IRQ_HANDLED)
status |= action->flags;
retval |= ret;
action = action->next;
} while (action);

if (status & IRQF_SAMPLE_RANDOM)
add_interrupt_randomness(irq);
local_irq_disable();

return retval;
}

Thanks,

Rajat
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Re: Use of IRQF_DISABLED along with IRQF_SHARED

sorry, i am also quite confused....

the caller of your function handle_IRQ_event() is __do_IRQ(), which is thus:

if (likely(!(desc->status & IRQ_DISABLED))) {
action_ret = handle_IRQ_event(irq, desc->action);
if (!noirqdebug)
note_interrupt(irq, desc, action_ret);
}

so what it means that only when IRQ_DISABLED is NOT SET, then
handle_IRQ_event() will be called, simulating a software-based IRQ.

and so the above function WILL ALWAYS BE CALLED WITH IRQ_DISABLED NOT
SET (assuming there is no other caller of handle_IRQ_event()).

errhhhh?? Am i right?
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RE: Use of IRQF_DISABLED along with IRQF_SHARED

----Original Message----
From: Peter Teoh [mailto:htmldeveloper@gmail.com]
Sent: Friday, February 08, 2008 8:11 PM
To: Rajat Jain
Cc: kernelnewbies@nl.linux.org; linux-newbie@vger.kernel.org
Subject: Re: Use of IRQF_DISABLED along with IRQF_SHARED

> sorry, i am also quite confused....
>
> the caller of your function handle_IRQ_event() is __do_IRQ(), which
> is thus:
>
> if (likely(!(desc->status & IRQ_DISABLED))) {
> action_ret = handle_IRQ_event(irq,
> desc->action); if (!noirqdebug)
> note_interrupt(irq, desc, action_ret);
> }
>
> so what it means that only when IRQ_DISABLED is NOT SET, then
> handle_IRQ_event() will be called, simulating a software-based IRQ.
>
> and so the above function WILL ALWAYS BE CALLED WITH IRQ_DISABLED NOT
> SET (assuming there is no other caller of handle_IRQ_event()).
>
> errhhhh?? Am i right?


Hi Peter,

I think you are mistaken between IRQ_DISABLED & IRQF_DISABLED. My question was about IRQF_DISABLED.

Thanks,

Rajat
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ISR may be called with interrupts enabled (Was:"Use of IRQF_DISABLED along with IRQF_SHARED&quo

Hi,

Was wondering if I did not frame my question appropriately? Or it there a better place to discuss this?

Thanks,

Rajat

>
> This is regarding the following code in kernel/irq/handle.c. Consider
> the case of a shared IRQ line, where two handlers are registered such
> that first handler does not specify IRQF_DISABLED, but the second one
> does. But it seems both the handlers will be called IRQs ENABLED
> (which is certainly not what the second handler expects).
>
> I also checked but could not find anything that stops me from
> registering two shared ISRs - one with IRQF_DISABLED & another
> without this flag. Am I missing something here?
>
> irqreturn_t handle_IRQ_event(unsigned int irq, struct irqaction
> *action) {
> irqreturn_t ret, retval = IRQ_NONE;
> unsigned int status = 0;
>
> handle_dynamic_tick(action);
>
> if (!(action->flags & IRQF_DISABLED))
> local_irq_enable_in_hardirq();
>
> do {
> ret = action->handler(irq, action->dev_id);
> if (ret == IRQ_HANDLED)
> status |= action->flags;
> retval |= ret;
> action = action->next;
> } while (action);
>
> if (status & IRQF_SAMPLE_RANDOM)
> add_interrupt_randomness(irq);
> local_irq_disable();
>
> return retval;
> }
>
> Thanks,
>
> Rajat

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