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

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Message-ID: <CA+h21hoqkE2D03BHrFeU+STbK8pStRRFu+x7+9j2nwFf+EHJNg@mail.gmail.com>
Date:   Sat, 9 Nov 2019 17:21:51 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     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 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.

Thanks,
-Vladimir

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