netdev - Re: ethernet-phy-ieee802.3-c22 binding and reset-gpios

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Message-ID: <20200826085857.GO13023@pengutronix.de>
Date:   Wed, 26 Aug 2020 10:58:57 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     netdev@...r.kernel.org, Florian Fainelli <f.fainelli@...il.com>,
        Heiner Kallweit <hkallweit1@...il.com>, kernel@...gutronix.de
Subject: Re: ethernet-phy-ieee802.3-c22 binding and reset-gpios

Hi Andrew,

On Tue, Aug 25, 2020 at 03:14:00PM +0200, Andrew Lunn wrote:
> On Tue, Aug 25, 2020 at 11:09:33AM +0200, Sascha Hauer wrote:
> > Hi All,
> > 
> > I am using the ethernet phy binding here that looks like:
> > 
> > ethphy1: ethernet-phy@1 {
> > 	compatible = "ethernet-phy-ieee802.3-c22";
> > 	reg = <1>;
> > 	eee-broken-1000t;
> > 	reset-gpios = <&gpio4 2 GPIO_ACTIVE_LOW>;
> > };
> > 
> > It seems the "reset-gpios" is inherently broken in Linux.
> 
> Hi Sascha
> 
> I think it would be better to say, it does not do what people expect,
> rather than broken.
> 
> This code was developed for a PHY which needed to be reset after
> enumeration. That PHY did enumerate, either because it was not held in
> reset, or would still answer ID requests while held in reset.
> 
> It does however not work for PHYs which are held in reset during probe
> and won't enumerate. This is a known issues, but could be better
> documented.

I think the behaviour should rather be improved than documented.

> 
> > Is this the path to go or are there any other ideas how to solve
> > this issue?
> 
> There is two different reset gpios in DT. There is a per PHY reset,
> which you are trying to use. And a per MDIO bus reset, which should
> apply to all PHYs on the bus. This per bus reset works more as
> expected. If this works for you, you could use that.

Well there is only one phy connected to the bus, so it makes no
difference if I say the reset GPIO is for the whole bus or for a single
phy only. The per bus reset should work, but currently it doesn't. First
reason I found out that mdiobus_register() doesn't handle -EPROBE_DEFER
returned by the devm_gpiod_get_optional() properly, patch follows.
Second reason is that the phy is not detected (id read returns 0xffff)
when the reset is attached to the bus. So far I haven't found the reason
for that.

> 
> Otherwise, you need to modify of_mdiobus_register() to look in device
> tree while it is performing the scan and see if there is a reset
> property for each address on the bus. If so, take the device out of
> reset before reading the ID registers.

Ok.

Sascha

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