linux-kernel - Re: [PATCH] ARM: dts: ls1021a-tsn: Use interrupts for the SGMII PHYs

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Date:   Sat, 9 Nov 2019 22:05:49 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Alexander Stein <alexander.stein@...lbox.org>
Cc:     Vladimir Oltean <olteanv@...il.com>, shawnguo@...nel.org,
        mark.rutland@....com, devicetree@...r.kernel.org,
        leoyang.li@....com, robh+dt@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] ARM: dts: ls1021a-tsn: Use interrupts for the SGMII PHYs

On Sat, Nov 09, 2019 at 08:52:54PM +0100, Alexander Stein wrote:
>  On Saturday, November 9, 2019, 4:21:51 PM CET Vladimir Oltean wrote:
> > On 09/11/2019, Andrew Lunn <andrew@...n.ch> wrote:
> > > On Sat, Nov 09, 2019 at 12:56:42PM +0200, Vladimir Oltean wrote:
> > >> On the LS1021A-TSN board, the 2 Atheros AR8031 PHYs for eth0 and eth1
> > >> have interrupt lines connected to the shared IRQ2_B LS1021A pin.
> > >>
> > >> The interrupts are active low, but the GICv2 controller does not support
> > >> active-low and falling-edge interrupts, so the only mode it can be
> > >> configured in is rising-edge.
> > >
> > > Hi Vladimir
> > >
> > > So how does this work? The rising edge would occur after the interrupt
> > > handler has completed? What triggers the interrupt handler?
> > >
> > > 	Andrew
> > >
> > 
> > Hi Andrew,
> > 
> > I hope I am not terribly confused about this. I thought I am telling
> > the interrupt controller to raise an IRQ as a result of the
> > low-to-high transition of the electrical signal. Experimentation sure
> > seems to agree with me. So the IRQ is generated immediately _after_
> > the PHY has left the line in open drain and it got pulled up to Vdd.
> 

> It is correct GIC only supports raising edge and active-high. The
> IRQ[0:5] on ls1021a are a bit special though.  They not directly
> connected to GIC, but there is an optional inverter, enabled by
> default.

Ah, O.K. So configuring for a rising edge is actually giving a falling
edge. Which is why it works.

Actually supporting this correctly is going a cause some pain. I
wonder how many DT files currently say rising/active high, when in
fact falling/active low is actually being used? And when the IRQ
controller really does support active low and falling, things brake?

Vladimir, since this is a shared interrupt, you really should use
active low here. Maybe the first step is to get control of the
inverter, and define a DT binding which is not going to break
backwards compatibility. And then wire up this interrupt.

	  Andrew