linux-kernel - Re: PHY reset question

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Date:   Mon, 12 Oct 2020 10:25:46 +0200
From:   Marek Vasut <marex@...x.de>
To:     Oleksij Rempel <o.rempel@...gutronix.de>,
        Bruno Thomsen <bruno.thomsen@...il.com>
Cc:     Fabio Estevam <festevam@...il.com>, Andrew Lunn <andrew@...n.ch>,
        David Jander <david@...tonic.nl>,
        Sascha Hauer <kernel@...gutronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: PHY reset question

On 10/12/20 7:48 AM, Oleksij Rempel wrote:
> Hi all,
> 
> thank you for the feedback!
> 
> On Fri, Oct 09, 2020 at 04:25:49PM +0200, Bruno Thomsen wrote:
>> Hi Fabio and Oleksij
>>
>> Den ons. 7. okt. 2020 kl. 11.50 skrev Fabio Estevam <festevam@...il.com>:
>>>
>>> Hi Oleksij,
>>>
>>> On Tue, Oct 6, 2020 at 5:05 AM Oleksij Rempel <o.rempel@...gutronix.de> wrote:
>>>>
>>>> Hello PHY experts,
>>>>
>>>> Short version:
>>>> what is the proper way to handle the PHY reset before identifying PHY?
>>>>
>>>> Long version:
>>>> I stumbled over following issue:
>>>> If PHY reset is registered within PHY node. Then, sometimes,  we will not be
>>>> able to identify it (read PHY ID), because PHY is under reset.
>>>>
>>>> mdio {
>>>>         compatible = "virtual,mdio-gpio";
>>>>
>>>>         [...]
>>>>
>>>>         /* Microchip KSZ8081 */
>>>>         usbeth_phy: ethernet-phy@3 {
>>>>                 reg = <0x3>;
>>>>
>>>>                 interrupts-extended = <&gpio5 12 IRQ_TYPE_LEVEL_LOW>;
>>>>                 reset-gpios = <&gpio5 11 GPIO_ACTIVE_LOW>;
>>>>                 reset-assert-us = <500>;
>>>>                 reset-deassert-us = <1000>;
>>>>         };
>>>>
>>>>         [...]
>>>> };
>>>>
>>>> On simple boards with one PHY per MDIO bus, it is easy to workaround by using
>>>> phy-reset-gpios withing MAC node (illustrated in below DT example), instead of
>>>> using reset-gpios within PHY node (see above DT example).
>>>>
>>>> &fec {
>>>>         [...]
>>>>         phy-mode = "rmii";
>>>>         phy-reset-gpios = <&gpio4 12 GPIO_ACTIVE_LOW>;
>>>>         [...]
>>>
>>> I thought this has been fixed by Bruno's series:
>>> https://www.spinics.net/lists/netdev/msg673611.html
>>
>> Yes, that has fixed the Microchip/Micrel PHY ID auto detection
>> issue. I have send a DTS patch v3 that makes use of the newly
>> added device tree parameter:
>> https://lkml.org/lkml/2020/9/23/595
> 
> This way is suitable only for boards with single PHY and single reset
> line. But it is not scale on boards with multiple PHY and multiple reset
> lines.
> 
> So far, it looks like using compatible like "ethernet-phy-idXXXX.XXXX"
> is the only way to go.

I did further digging in this, and I agree it is either this or reset in
boot loader, sigh.