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SubjectRE: [PATCH] net: fec: defer probe if PHY on external MDIO bus is not available
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Hi Matthias,

> -----Original Message-----
> From: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> Sent: 2021年10月14日 19:31
> To: Joakim Zhang <qiangqing.zhang@nxp.com>; David S. Miller
> <davem@davemloft.net>; Jakub Kicinski <kuba@kernel.org>
> Cc: netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Matthias Schiffer
> <matthias.schiffer@ew.tq-group.com>
> Subject: [PATCH] net: fec: defer probe if PHY on external MDIO bus is not
> available
>
> On some SoCs like i.MX6UL it is common to use the same MDIO bus for PHYs
> on both Ethernet controllers. Currently device trees for such setups have to
> make assumptions regarding the probe order of the controllers:
>
> For example in imx6ul-14x14-evk.dtsi, the MDIO bus of fec2 is used for the
> PHYs of both fec1 and fec2. The reason is that fec2 has a lower address than
> fec1 and is thus loaded first, so the bus is already available when fec1 is
> probed.

It's not correct, I think, we have board designed to use fec1(which is lower address) to controller MDIO interface, such as,
https://source.codeaurora.org/external/imx/linux-imx/tree/arch/arm64/boot/dts/freescale/imx8qm-mek.dts?h=lf-5.10.y#n948
that means our driver can handle these cases, not related to the order.

> Besides being confusing, this limitation also makes it impossible to use the
> same device tree for variants of the i.MX6UL with one Ethernet controller
> (which have to use the MDIO of fec1, as fec2 does not exist) and variants with
> two controllers (which have to use fec2 because of the load order).

Generally speaking, you should only include imx6ul.dtsi for your board design to cover SoC definition,
and imx6ul-14x14-evk.dtsi/ imx6ul-14x14-evk.dts is for our 14x14 EVK board. So do we really need this
defer probe?

>
> To fix this, defer the probe of the Ethernet controller when the PHY is not on
> our own MDIO bus and not available.
>
> Signed-off-by: Matthias Schiffer <matthias.schiffer@ew.tq-group.com>
> ---
> drivers/net/ethernet/freescale/fec_main.c | 23 ++++++++++++++++++++++-
> 1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index 47a6fc702ac7..dc070dd216e8 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -3820,7 +3820,28 @@ fec_probe(struct platform_device *pdev)
> goto failed_stop_mode;
>
> phy_node = of_parse_phandle(np, "phy-handle", 0);
> - if (!phy_node && of_phy_is_fixed_link(np)) {
> + if (phy_node) {
> + struct device_node *mdio_parent =
> + of_get_next_parent(of_get_parent(phy_node));
> +
> + ret = 0;
> +
> + /* Skip PHY availability check for our own MDIO bus to avoid
> + * cyclic dependency
> + */
> + if (mdio_parent != np) {
> + struct phy_device *phy = of_phy_find_device(phy_node);
> +
> + if (phy)
> + put_device(&phy->mdio.dev);
> + else
> + ret = -EPROBE_DEFER;
> + }
> +
> + of_node_put(mdio_parent);
> + if (ret)
> + goto failed_phy;
> + } else if (of_phy_is_fixed_link(np)) {
> ret = of_phy_register_fixed_link(np);
> if (ret < 0) {
> dev_err(&pdev->dev,
> --
> 2.17.1

Best Regards,
Joakim Zhang
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