Re: [PATCH 4/4] ARM: dts: vf610-zii-dev-rev-b: add interrupts for 88e1545 PHY

[Russell King - ARM Linux <linux-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>]

On Thu, Dec 21, 2017 at 02:40:58PM +0100, Andrew Lunn wrote:
> On Thu, Dec 21, 2017 at 01:32:21PM +0100, Linus Walleij wrote:
> > On Thu, Dec 21, 2017 at 12:12 AM, Russell King
> > <rmk+kernel-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org> wrote:
> > 
> > > The 88e1545 PHY has its interrupts wired to the VF610, so we might as
> > > well use them.
> > >
> > > Signed-off-by: Russell King <rmk+kernel-I+IVW8TIWO2tmTQ+vhA3Yw@public.gmane.org>
> > > ---
> > > This is certainly not correct, as all PHYs on this device share the
> > > same interrupt line, but we can't specify the pinmux settings
> > > individually on each PHY.  How should this be handled?
> > 
> > I do not know the details of the Marvell switch.
> 
> Hi Linus
> 
> The 88e1545 is a discreet quad PHY. It is connected to the switch, but
> not integrated into the switch. All its interrupt handling is done
> with a GPIO onto the Freescale processor, via a GPIO. There is nothing
> DSA related here at all with respect to the interrupt. It is just a
> normal GPIO interrupt. What is a bit odd is that it one shared
> interrupt for all four PHYs.
> 
> What you described with an irqchip inside the switch is what we
> actually do for the internal PHYs on Marvell devices. And it is what i
> recommend for all DSA drivers. Expose standard IRQs, and let phylib
> use them in its normal way.

... and it has to be said that model doesn't work in this case,
because, although there is the possibility to demux the interrupt
any of the PHYs, you already need to be driving one of the PHYs.

It's not an interrupt controller itself (there's no possibility to
enable/disable individual interrupts from a PHY) so it doesn't make
sense.

What we have here is _really_ a shared interrupt between four
separate devices, and we need a way to sanely describe resources
shared between several device instances to pinmux.  Unfortunately,
it seems pinmux is designed around one device having exclusive use
of a resource, which makes it hard to describe shared interrupts in
DT.

Given that DT should be a description of the hardware, and should be
independent of the OS implementation, I'd say this is a pinmux bug,
because pinmux gets in the way of describing the hardware correctly.
;)

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