linux-kernel - Re: [PATCH v2] arm64: dts: ti: k3-am654-icssg2: Enable PHY interrupts for ICSSG2

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Message-ID: <20231214121727.ayrbqz2nmeb25rpw@striving>
Date:   Thu, 14 Dec 2023 06:17:27 -0600
From:   Nishanth Menon <nm@...com>
To:     Siddharth Vadapalli <s-vadapalli@...com>
CC:     <vigneshr@...com>, <kristo@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <conor+dt@...nel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <danishanwar@...com>,
        <r-gunasekaran@...com>, <srk@...com>
Subject: Re: [PATCH v2] arm64: dts: ti: k3-am654-icssg2: Enable PHY
 interrupts for ICSSG2

On 11:14-20231214, Siddharth Vadapalli wrote:
> Hello Nishanth,
> 
> On 13/12/23 18:08, Nishanth Menon wrote:
> > On 13:32-20231213, Siddharth Vadapalli wrote:
> >> Enable interrupt mode of operation of the DP83867 Ethernet PHY which is
> >> used by ICSSG2. The DP83867 PHY driver already supports interrupt handling
> >> for interrupts generated by the PHY. Thus, add the necessary device-tree
> >> support to enable it.
> >>
> >> Since the GPIO1_87 line is muxed with EXT_REFCLK1 and SYNC1_OUT, update
> >> the pinmux to select GPIO1_87 for routing the interrupt.
> >>
> >> As the same interrupt line and therefore the same pinmux configuration is
> >> applicable to both Ethernet PHYs used by ICSSG2, allocate the pinmux
> >> resource to the first Ethernet PHY alone.
> 
> ...
> 
> > 
> > https://www.ti.com/lit/ds/symlink/dp83867ir.pdf -> it looks like the
> > interrupt pin is level event. but drivers/gpio/gpio-davinci.c::
> > gpio_irq_type() -> The SoC cannot handle level, only edge.
> > 
> > A bit confused here..  GPIO 87 is shared between two phys. isn't it a
> > case of race?
> > 
> > PHY1 assets low
> > phy1 handler starts, but before the driver it clears the condition:
> > PHY2 asserts low - but since the signal is already low, there is no
> > pulse
> > phy1 handler clears phy1 condition, but signal is still low due to phy2?
> > now phy2 OR phy1 never gets handled since there is never a pulse event
> > ever again.
> 
> Yes, you are right! Edge-Triggered interrupts shouldn't be shared. I missed
> noticing this. Thank you for pointing it out. Since the SoC only supports
> Edge-Triggered interrupts, I believe that the correct decision would be to use
> the interrupt for only one of the two PHYs, while leaving the other PHY in
> polled mode of operation which is the default.
> 
> Kindly let me know if this is acceptable and I shall update this patch accordingly.

Sounds like a bug in board design there (due to an choice of IP
limitation) - I suggest getting it noted in board documentation and
refer to the errata in the second phy (else folks will wonder why we
aren't using interrupts on the second phy.

> 
> > 
> > 
> >>  		ti,rx-internal-delay = <DP83867_RGMIIDCTL_2_00_NS>;
> >>  		ti,fifo-depth = <DP83867_PHYCR_FIFO_DEPTH_4_B_NIB>;
> >>  	};
> >> -- 
> >> 2.34.1
> >>
> > 
> 
> -- 
> Regards,
> Siddharth.

-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D