Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip
From: Boris Brezillon
Date: Mon Feb 23 2015 - 12:01:18 EST
Thanks for the clarification, and sorry if I've been a bit harsh to you
in my previous answer, but this whole shared irq thing is starting to
drive me crazy.
On Fri, 20 Feb 2015 15:16:56 +0000
Mark Rutland <mark.rutland@xxxxxxx> wrote:
> An IRQ cannot be shared between a device with IRQF_NO_SUSPEND and a
> device that wishes to operate as a wakeup device, because the semantics
> don't align. One wishes to handle IRQs continuously and one wants to
> abort suspend at the first IRQ (waiting until part-way through the
> resume before handling it).
> So those devices above which wish to operate as wakeup devices are
> either irrelevant or unsalvageable with the current approaches.
> The flag or demux chip only happens to mask the problem in the absence
> of strict sanity checking.
> If you want to be able to share the line then you will need to
> fundamentally rework the way wakeup interrupts work in order to be able
> to decide when you've encountered a real wakeup event.
Okay, I'll try to summarize the discussion we had on IRC regarding this
On at91 platforms, irq line 1 is shared by a timer (PIT) and some
devices that can register themselves as wakeup sources (especially the
I doubt at91 users will agree on dropping either of these features (the
timer or the wakeup on RTC/UART/...), so, can we try to find a solution
that would both make irq, DT and at91 guys happy (that doesn't sound
like an easy task :-)) ?
The whole problem here is that we can't have both IRQF_NO_SUSPEND flag
set on one of the shared action and others that are configuring the irq
as a wakeup source, because it would always lead to the system being
woken up (even when the only thing we were supposed to do is handle the
This is because irq_may_run , which is called to decide whether we
should handle this irq or just wake the system up , will always
return true if at least one of the shared action has tagged the irq
line as a wakeup source.
Sorry for summarizing things you most likely already know, but I want
to be sure I'm actually understanding it correctly.
Now, let's look at how this could be solved.
Here is a proposal  that does the following:
1/ prevent a system wakeup when at least one of the action handler
has set the IRQF_NO_SUSPEND flag
2/ Add a few helpers to deal with system wakeup from drivers code
3/ Rework the at91 RTC driver to show how such weird cases could be
Of course, I'll need the IRQF_SHARED_TIMER_OK patch to prevent the
Please, let me know if I missed anything important, share your opinion
on this proposal, and feel free to propose any other solution.
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
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