linux-kernel - Re: [PATCH RESEND net] net: phy: xgmiitorgmii: Support generic PHY status read

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Message-ID: <12abec9f-29a8-7dfc-b7cc-59be34e1b6d7@xilinx.com>
Date:   Mon, 11 Mar 2019 13:51:18 +0100
From:   Michal Simek <michal.simek@...inx.com>
To:     Harini Katakam <harinik@...inx.com>, Andrew Lunn <andrew@...n.ch>
CC:     Michal Simek <michal.simek@...inx.com>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        <netdev@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Heiner Kallweit <hkallweit1@...il.com>
Subject: Re: [PATCH RESEND net] net: phy: xgmiitorgmii: Support generic PHY
 status read

On 11. 03. 19 13:27, Harini Katakam wrote:
> Hi Andrew,
> On Mon, Mar 11, 2019 at 11:34 AM Harini Katakam <harinik@...inx.com> wrote:
>>
>> Hi Andrew,
>> On Sat, Mar 9, 2019 at 9:53 PM Andrew Lunn <andrew@...n.ch> wrote:
>>>
>>>> Related to this, I have a query on how the DT node for gmii2rgmii should look.
>>>> One of the users of gmii2rgmii is Cadence macb driver. In Xilinx tree, we use
>>>> this piece of code to register this mdiobus:
>>>> + mdio_np = of_get_child_by_name(np, "mdio");
>>>> + if (mdio_np) {
>>>> + of_node_put(mdio_np);
>>>> + err = of_mdiobus_register(bp->mii_bus, mdio_np);
>>>> + if (err)
>>>> + goto err_out_unregister_bus;
>>>>
>>>> And the DT node looks like this:
>>>> ethernet {
>>>>     phy-mode = "gmii";
>>>>     phy-handle = <&extphy>;
>>>>
>>>>     mdio {
>>>>         extphy {
>>>>             reg = <x>;
>>>>         };
>>>>         gmii_to_rgmii{
>>>>             compatible = "xlnx,gmii-to-rgmii-1.0";
>>>>             phy-handle = <&extphy>;
>>>>             reg = <x>;
>>>>         };
>>>>     };
>>>> };
>>>
>>> Hi Harini
>>>
>>> You have this setup:
>>>
>>> MAC <==> GMII2RGMII <==> RGMII_PHY
>>>
>>> So you want the MAC phy-handle to point to the gmii_to_rgmii 'PHY'.
>>>
>>> Feel free to submit a patch extending
>>> Documentation/devicetree/bindings/net/xilinx_gmii2rgmii.txt to include
>>> a MAC node, etc.
>>
>> Thank you, will do the same.
> 
> Thanks again for your input. So, I did some testing with this change.
> But the issue is that, if I point the phy-handle to gmi2rgmii,
> of_phy_connect will be called from the MAC and it will fail because gmii2rgmii
> is not a PHY driver and it does not have a standard PHY register set or ID.
> Which goes back to the discussion above whether this needs to changed in the IP.
> 
> But right now, it is a bridge device on the MDIO bus and has no PHY
> functionality.
> Moreover, any MAC is capable of accessing the external PHY with no interference
> in the MDIO path (the gmii2rgmii bridge just acts like another device
> on a common bus).
> 
> What Michal suggested below in uboot is that they register gmii2rgmii
> with a dummy
> PHY ID and then attach the external phy driver in its probe. I'm not
> sure if this will work
> in linux i.e. calling phy_connect_direct inside the gmii2rgmii probe.

In u-boot behavior and wiring is similar to fixed-link phy.

Thanks,
Michal