netdev - Re: [PATCH v3 2/2] net: axiemac: use a phandle to reference pcs

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Date:   Fri, 18 Mar 2022 16:58:29 +0000
From:   Robert Hancock <robert.hancock@...ian.com>
To:     "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "andy.chiu@...ive.com" <andy.chiu@...ive.com>,
        "radhey.shyam.pandey@...inx.com" <radhey.shyam.pandey@...inx.com>
CC:     "andrew@...n.ch" <andrew@...n.ch>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "greentime.hu@...ive.com" <greentime.hu@...ive.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: Re: [PATCH v3 2/2] net: axiemac: use a phandle to reference pcs_phy

On Fri, 2022-03-18 at 15:00 +0800, Andy Chiu wrote:
> In some SGMII use cases where both a fixed link external PHY and the
> internal PCS/PMA PHY need to be configured, we should explicitly use a
> phandle "pcs-phy" to get the reference to the PCS/PMA PHY. Otherwise, the
> driver would use "phy-handle" in the DT as the reference to both the
> external and the internal PCS/PMA PHY.
> 
> In other cases where the core is connected to a SFP cage, we could still
> point phy-handle to the intenal PCS/PMA PHY, and let the driver connect
> to the SFP module, if exist, via phylink.
> 
> Fixes: 1a02556086fc (net: axienet: Properly handle PCS/PMA PHY for 1000BaseX
> mode)
> Signed-off-by: Andy Chiu <andy.chiu@...ive.com>
> Reviewed-by: Greentime Hu <greentime.hu@...ive.com>
> ---
>  drivers/net/ethernet/xilinx/xilinx_axienet_main.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 6fd5157f0a6d..6f81d756e6c8 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -2078,7 +2078,17 @@ static int axienet_probe(struct platform_device *pdev)
>  			ret = -EINVAL;
>  			goto cleanup_mdio;
>  		}
> -		lp->pcs_phy = of_mdio_find_device(lp->phy_node);
> +		np = of_parse_phandle(pdev->dev.of_node, "pcs-handle", 0);
> +		if (np) {
> +			lp->pcs_phy = of_mdio_find_device(np);
> +			of_node_put(np);
> +		} else {
> +			/* Deprecated: Always use "pcs-handle" for pcs_phy.
> +			 * Falling back to "phy-handle" here is only for
> +			 * backward compatibility with old device trees.
> +			 */
> +			lp->pcs_phy = of_mdio_find_device(lp->phy_node);
> +		}
>  		if (!lp->pcs_phy) {
>  			ret = -EPROBE_DEFER;
>  			goto cleanup_mdio;

I think there are a few other changes in surrounding code required for this to
work as expected:

-The call to axienet_mdio_setup should not be conditional on whether phy_node
is set

-The code is currently failing out if phy-handle is not set, it should be
satisfied if either phy-handle or pcs-handle are set.

-I'm not actually sure why phy_node is being stored in the device structure
rather than just doing an of_node_put on it right away after use, it doesn't
look like anything else uses it after initialization. Might be a remnant of
older code that could be changed to be treated the same as pcs-handle here.

-- 
Robert Hancock
Senior Hardware Designer, Calian Advanced Technologies
www.calian.com