Re: [PATCH net-next v2] net: stmmac: don't create a MDIO bus if unnecessary
From: Andrew Halaney
Date: Thu Dec 07 2023 - 08:32:39 EST
On Thu, Dec 07, 2023 at 02:56:25PM +0300, Serge Semin wrote:
> Hi Andrew
>
> On Wed, Dec 06, 2023 at 05:46:09PM -0600, Andrew Halaney wrote:
> > The stmmac_dt_phy() function, which parses the devicetree node of the
> > MAC and ultimately causes MDIO bus allocation, misinterprets what
> > fixed-link means in relation to the MAC's MDIO bus. This results in
> > a MDIO bus being created in situations it need not be.
> >
> > Currently a MDIO bus is created if the description is either:
> >
> > 1. Not fixed-link
> > 2. fixed-link but contains a MDIO bus as well
> >
> > The "1" case above isn't always accurate. If there's a phy-handle,
> > it could be referencing a phy on another MDIO controller's bus[1]. In
> > this case currently the MAC will make a MDIO bus and scan it all
> > anyways unnecessarily.
> >
> > There's also a lot of upstream devicetrees[2] that expect a MDIO bus to
> > be created and scanned for a phy. This case can also be inferred from
> > the platform description by not having a phy-handle && not being
> > fixed-link. This hits case "1" in the current driver's logic.
> >
> > Let's improve the logic to create a MDIO bus if either:
> >
> > - Devicetree contains a MDIO bus
> > - !fixed-link && !phy-handle (legacy handling)
> >
> > Below upstream devicetree snippets can be found that explain some of
> > the cases above more concretely.
> >
> > Here's[0] a devicetree example where the MAC is both fixed-link and
> > driving a switch on MDIO (case "2" above). This needs a MDIO bus to
> > be created:
> >
> > &fec1 {
> > phy-mode = "rmii";
> >
> > fixed-link {
> > speed = <100>;
> > full-duplex;
> > };
> >
> > mdio1: mdio {
> > switch0: switch0@0 {
> > compatible = "marvell,mv88e6190";
> > pinctrl-0 = <&pinctrl_gpio_switch0>;
> > };
> > };
> > };
> >
> > Here's[1] an example where there is no MDIO bus or fixed-link for
> > the ethernet1 MAC, so no MDIO bus should be created since ethernet0
> > is the MDIO master for ethernet1's phy:
> >
> > ðernet0 {
> > phy-mode = "sgmii";
> > phy-handle = <&sgmii_phy0>;
> >
> > mdio {
> > compatible = "snps,dwmac-mdio";
> > sgmii_phy0: phy@8 {
> > compatible = "ethernet-phy-id0141.0dd4";
> > reg = <0x8>;
> > device_type = "ethernet-phy";
> > };
> >
> > sgmii_phy1: phy@a {
> > compatible = "ethernet-phy-id0141.0dd4";
> > reg = <0xa>;
> > device_type = "ethernet-phy";
> > };
> > };
> > };
> >
> > ðernet1 {
> > phy-mode = "sgmii";
> > phy-handle = <&sgmii_phy1>;
> > };
> >
> > Finally there's descriptions like this[2] which don't describe the
> > MDIO bus but expect it to be created and the whole address space
> > scanned for a phy since there's no phy-handle or fixed-link described:
> >
> > &gmac {
> > phy-supply = <&vcc_lan>;
> > phy-mode = "rmii";
> > snps,reset-gpio = <&gpio3 RK_PB4 GPIO_ACTIVE_HIGH>;
> > snps,reset-active-low;
> > snps,reset-delays-us = <0 10000 1000000>;
> > };
> >
> > [0] https://elixir.bootlin.com/linux/v6.5-rc5/source/arch/arm/boot/dts/nxp/vf/vf610-zii-ssmb-dtu.dts
> > [1] https://elixir.bootlin.com/linux/v6.6-rc5/source/arch/arm64/boot/dts/qcom/sa8775p-ride.dts
> > [2] https://elixir.bootlin.com/linux/v6.6-rc5/source/arch/arm64/boot/dts/rockchip/rk3368-r88.dts#L164
>
> Thank you for the patch. Please find a comment below.
>
> >
> > Co-developed-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
> > Signed-off-by: Andrew Halaney <ahalaney@xxxxxxxxxx>
> > ---
> > .../net/ethernet/stmicro/stmmac/stmmac_platform.c | 85 ++++++++++------------
> > 1 file changed, 37 insertions(+), 48 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > index 1ffde555da47..7da461fe93f6 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_platform.c
> > @@ -296,69 +296,39 @@ static int stmmac_mtl_setup(struct platform_device *pdev,
> > }
> >
> > /**
> > - * stmmac_dt_phy - parse device-tree driver parameters to allocate PHY resources
> > - * @plat: driver data platform structure
> > - * @np: device tree node
> > - * @dev: device pointer
> > - * Description:
> > - * The mdio bus will be allocated in case of a phy transceiver is on board;
> > - * it will be NULL if the fixed-link is configured.
> > - * If there is the "snps,dwmac-mdio" sub-node the mdio will be allocated
> > - * in any case (for DSA, mdio must be registered even if fixed-link).
> > - * The table below sums the supported configurations:
> > - * -------------------------------
> > - * snps,phy-addr | Y
> > - * -------------------------------
> > - * phy-handle | Y
> > - * -------------------------------
> > - * fixed-link | N
> > - * -------------------------------
> > - * snps,dwmac-mdio |
> > - * even if | Y
> > - * fixed-link |
> > - * -------------------------------
> > + * stmmac_of_get_mdio() - Gets the MDIO bus from the devicetree
> > + * @np: devicetree node
> > *
> > - * It returns 0 in case of success otherwise -ENODEV.
> > + * The MDIO bus will be searched for in the following ways:
> > + * 1. The compatible is "snps,dwc-qos-ethernet-4.10" && a "mdio" named
> > + * child node exists
> > + * 2. A child node with the "snps,dwmac-mdio" compatible is present
> > + *
> > + * Return: The MDIO node if present otherwise NULL
> > */
> > -static int stmmac_dt_phy(struct plat_stmmacenet_data *plat,
> > - struct device_node *np, struct device *dev)
> > +static struct device_node *stmmac_of_get_mdio(struct device_node *np)
> > {
> > - bool mdio = !of_phy_is_fixed_link(np);
> > static const struct of_device_id need_mdio_ids[] = {
> > { .compatible = "snps,dwc-qos-ethernet-4.10" },
> > {},
> > };
> > + struct device_node *mdio_node = NULL;
> >
> > if (of_match_node(need_mdio_ids, np)) {
> > - plat->mdio_node = of_get_child_by_name(np, "mdio");
> > + mdio_node = of_get_child_by_name(np, "mdio");
> > } else {
> > /**
> > * If snps,dwmac-mdio is passed from DT, always register
> > * the MDIO
> > */
> > - for_each_child_of_node(np, plat->mdio_node) {
> > - if (of_device_is_compatible(plat->mdio_node,
> > + for_each_child_of_node(np, mdio_node) {
> > + if (of_device_is_compatible(mdio_node,
> > "snps,dwmac-mdio"))
> > break;
> > }
> > }
> >
> > - if (plat->mdio_node) {
> > - dev_dbg(dev, "Found MDIO subnode\n");
> > - mdio = true;
> > - }
> > -
> > - if (mdio) {
> > - plat->mdio_bus_data =
> > - devm_kzalloc(dev, sizeof(struct stmmac_mdio_bus_data),
> > - GFP_KERNEL);
> > - if (!plat->mdio_bus_data)
> > - return -ENOMEM;
> > -
> > - plat->mdio_bus_data->needs_reset = true;
> > - }
> > -
> > - return 0;
> > + return mdio_node;
> > }
> >
> > /**
> > @@ -417,6 +387,7 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac)
> > struct device_node *np = pdev->dev.of_node;
> > struct plat_stmmacenet_data *plat;
> > struct stmmac_dma_cfg *dma_cfg;
> > + bool legacy_mdio;
> > int phy_mode;
> > void *ret;
> > int rc;
> > @@ -471,10 +442,28 @@ stmmac_probe_config_dt(struct platform_device *pdev, u8 *mac)
> > if (of_property_read_u32(np, "snps,phy-addr", &plat->phy_addr) == 0)
> > dev_warn(&pdev->dev, "snps,phy-addr property is deprecated\n");
> >
> > - /* To Configure PHY by using all device-tree supported properties */
> > - rc = stmmac_dt_phy(plat, np, &pdev->dev);
> > - if (rc)
> > - return ERR_PTR(rc);
> > + plat->mdio_node = stmmac_of_get_mdio(np);
> > + if (plat->mdio_node)
> > + dev_dbg(&pdev->dev, "Found MDIO subnode\n");
> > +
>
> > + /* Legacy devicetrees allowed for no MDIO bus description and expect
> > + * the bus to be scanned for devices. If there's no phy or fixed-link
> > + * described assume this is the case since there must be something
> > + * connected to the MAC.
> > + */
> > + legacy_mdio = !of_phy_is_fixed_link(np) && !plat->phy_node;
> > + if (legacy_mdio)
> > + dev_info(&pdev->dev, "Deprecated MDIO bus assumption used\n");
> > +
> > + if (plat->mdio_node || legacy_mdio) {
> > + plat->mdio_bus_data = devm_kzalloc(&pdev->dev,
> > + sizeof(struct stmmac_mdio_bus_data),
> > + GFP_KERNEL);
> > + if (!plat->mdio_bus_data)
> > + return ERR_PTR(-ENOMEM);
> > +
> > + plat->mdio_bus_data->needs_reset = true;
> > + }
>
> Why did you decide to move this out of the dedicated function?
> stmmac_probe_config_dt() is already overwhelmed with various
> non-coherent actions. The method has already got to being too long to
> follow the kernel coding style limit (I have got a not submitted yet
> cleanup patchset which step-by-step fixes that). Could you please get
> the chunk above back to the respective function and, for instance,
> just change it's name to something like stmmac_mdio_setup()? (I prefer
> having "_setup" suffix because some of the locally defined static
> methods already use it: stmmac_axi_setup(), stmmac_mtl_setup().)
Sure, I can put it back in. I'll probably keep stmmac_of_get_mdio()
(which is named in the style I see in the current file -- although as
you highlight that shouldn't be taken as the best example of clean),
and have stmmac_mdio_setup() call that and and mimic the inputs/outputs
of the current function (moving the rest of the added code from
stmmac_probe_config_dt() back into that function).
Thanks for the feedback, let me know if you still think that abstraction
isn't ideal (or wait till I post it :P) and I'll go with exactly as you
said. I'm not _too_ opinionated on it, but thought stmmac_dt_phy()
didn't explain much and stmmac_of_get_mdio() was self-explanatory enough
that it helped readability.
>
> -Serge(y)
>
> >
> > of_property_read_u32(np, "tx-fifo-depth", &plat->tx_fifo_size);
> >
> >
> > ---
> > base-commit: fd8a79b63710acb84321be3ce74be23c876873fb
> > change-id: 20231127-stmmac-no-mdio-node-1db9da8a25d9
> >
> > Best regards,
> > --
> > Andrew Halaney <ahalaney@xxxxxxxxxx>
> >
> >
>