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

On Sat, Nov 09, 2019 at 05:16:48PM +0200, Vladimir Oltean wrote:

On Saturday, 9 November 2019, Andrew Lunn [off-list ref] wrote:

quoted

On Sat, Nov 09, 2019 at 12:56:42PM +0200, Vladimir Oltean wrote:

quoted

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.

Hi Vladimir

                       t1                    t2

     ------------------\                     /----------------
                        \-------------------/

The interrupt output is active low. So it is high by default. At time
t1 something happens, say the link is established. The interrupt
becomes active, we have a failing edge. We want the interrupt
controller to fire. Lets say it does. The interrupt handler runs, and
clears the interrupt cause. This is at time t2. We then get a rising
edge and the PHY releases the interrupt, and the level returns to
high.

So how does this work if you have the interrupt controller triggering
on a rising edge? The edge won't rise until the interrupt handler
finishes its work.

	 Andrew