Re: [PATCH v4 3/5] irqchip: Add DT binding doc for the virtual irq demuxer chip

[Boris Brezillon <boris.brezillon@free-electrons.com>]

On Tue, 10 Feb 2015 16:16:00 +0000
Mark Rutland <mark.rutland@arm.com> wrote:

> On Tue, Feb 10, 2015 at 03:52:01PM +0000, Boris Brezillon wrote:
> > Hi Mark,
> > 
> > On Tue, 10 Feb 2015 15:36:28 +0000
> > Mark Rutland <mark.rutland@arm.com> wrote:
> > 
> > > Hi Boris,
> > > 
> > > On Thu, Jan 29, 2015 at 10:33:38AM +0000, Boris Brezillon wrote:
> > > > Add documentation for the virtual irq demuxer.
> > > > 
> > > > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > > > Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
> > > > ---
> > > >  .../bindings/interrupt-controller/dumb-demux.txt   | 41 ++++++++++++++++++++++
> > > >  1 file changed, 41 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > > > new file mode 100644
> > > > index 0000000..b9a7830
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/interrupt-controller/dumb-demux.txt
> > > > @@ -0,0 +1,41 @@
> > > > +* Virtual Interrupt Demultiplexer
> > > > +
> > > > +This virtual demultiplexer simply forward all incoming interrupts to its
> > > > +enabled/unmasked children.
> > > > +It is only intended to be used by hardware that do not provide a proper way
> > > > +to demultiplex a source interrupt, and thus have to wake all their children
> > > > +up so that they can possibly handle the interrupt (if needed).
> > > > +This can be seen as an alternative to shared interrupts when at least one
> > > > +of the interrupt children is a timer (and require the irq to stay enabled
> > > > +on suspend) while others are not. This will prevent calling irq handlers of
> > > > +non timer devices while they are suspended.
> > > 
> > > This sounds like a DT-workaround for a Linux implementation problem, and
> > > I don't think this the right way to solve your problem.
> > 
> > I understand your concern, but why are you answering while I asked for
> > DT maintainers reviews for several days (if not several weeks).
> 
> I am sorry that I did not spot those, and I am very sorry that this
> means I am only now able to air my concerns.
> 
> > > Why does this have to be in DT at all? Why can we not fix the core to
> > > handle these details?
> > 
> > We already discussed that with Rob and Thomas, and hiding such a
> > demuxer chip is not an easy task.
> > I'm open to any suggestion to do that, though I'd like you (I mean DT
> > guys) to provide a working implementation (or at least a viable concept)
> > that would silently demultiplex an irq.
> 
> Is it truly necessary to drop a emux in the middle?
> 
> As far as I can see, all that we're attempting to do here is hide the
> IRQF_NO_SUSPEND mismatch from the core IRQ code, though I've only just
> started digging and haven't yet figured out where/why the core code
> cares. Any hints?

You should have a look at this thread [1] ;-)

[1]https://lkml.org/lkml/2014/12/15/552

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com