Re: [PATCH 3/3] irqchip: orion: clear stale interrupts in irq_enable
From: Jason Gunthorpe
Date: Thu Jan 23 2014 - 17:52:25 EST
On Thu, Jan 23, 2014 at 11:38:06PM +0100, Sebastian Hesselbarth wrote:
> Bridge IRQ_CAUSE bits are asserted regardless of the corresponding bit in
> IRQ_MASK register. To avoid interrupt events on stale irqs, we have to clear
> them before unmask. This installs an .irq_enable callback to ensure stale
> irqs are cleared before initial unmask.
I'm not sure if putting this in irq_enable is correct. I think this
should only happen at irq_startup.
The question boils down to what is supposed to happen with this code
write(.. something to cause an interrupt edge ..);
.. synchronize ..
Do we get the interrupt or not?
I found this message from Linus long ago:
> Btw, the "disable_irq()/enable_irq()" subsystem has been written so that
> when you disable an edge-triggered interrupt, and the edge happens while
> the interrupt is disabled, we will re-play the interrupt at enable time.
> Exactly so that drivers can have an easier time and don't have to
> normally worry about whether something is edge or level-triggered.
And found this note in Documentation/DocBook/genericirq.tmpl:
> This prevents losing edge interrupts on hardware which does
> not store an edge interrupt event while the interrupt is disabled at
> the hardware level.
So I think it is very clear that the chip driver should not discard
edges that happened while the interrupt was disabled.
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