irq handling in DDE Linux26

Da Zheng zhengda1936 at
Wed May 12 11:36:36 CEST 2010

On 10-5-12 上午6:03, Samuel Thibault wrote:
> Da Zheng, le Sat 08 May 2010 23:19:08 +0800, a écrit :
>> A stupid question: when disable_irq_nosync is called, IRQ_DISABLED is set in the
>> irq descriptor in the Linux kernel and the corresponding hardirq line should be
>> masked as well (at least, it seems the kernel for x86 does so).
> AIUI, on unmask the hardware will trigger the interrupt that was raised
> by the hardware in the meanwhile. Which precise x86 file are you looking
> at? What do you exactly mean by "hardirq": the actual hardware chip or
> the software hardIRQ handler?
In disable_irq_nosync, there is code as follow:
                desc->status |= IRQ_DISABLED;
For the x86 platform, `disable' points to disable_8259A_irq. So when
disable_irq_nosync is called, IRQ_DISABLED is set and the irq line (the
hardware) is masked.
>> How can handle_edge_irq be called?
> AIUI, on hardware irq unmasking.
When hardware irq is unmasked, IRQ_DISABLED should have been removed. I meant,
how can handle_edge_irq be called when IRQ_DISABLED is still set? It seems to me
that IRQ_PENDING cannot be set in handle_edge_irq when the irq line is disabled.

Best regards,
Zheng Da

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