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From: Andrew Lunn <andrew@lunn.ch>
To: Saravana Kannan <saravanak@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	Vladimir Oltean <olteanv@gmail.com>,
	"David S. Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, Len Brown <lenb@kernel.org>,
	Alvin Sipraga <ALSI@bang-olufsen.dk>,
	kernel-team@android.com, linux-kernel@vger.kernel.org,
	netdev@vger.kernel.org, linux-acpi@vger.kernel.org
Subject: Re: [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT
Date: Fri, 27 Aug 2021 15:44:34 +0200	[thread overview]
Message-ID: <YSjsQmx8l4MXNvP+@lunn.ch> (raw)
In-Reply-To: <CAGETcx_r8LSxV5=GQ-1qPjh7qGbCqTsSoSkQfxAKL5q+znRoWg@mail.gmail.com>

> fw_devlink=on/device links short circuits the probe() call of a
> consumer (in this case the PHY) and returns -EPROBE_DEFER if the
> supplier's (in this case switch) probe hasn't finished without an
> error. fw_devlink/device links effectively does the probe in graph
> topological order and there's a ton of good reasons to do it that way
> -- what's why fw_devlink=on was implemented.
> 
> In this specific case though, since the PHY depends on the parent
> device, if we fail the parent's probe realtek_smi_probe() because the
> PHYs failed to probe, we'll get into a catch-22/chicken-n-egg
> situation and the switch/PHYs will never probe.

So lets look at:

arch/arm/boot/dts/vf610-zii-dev-rev-b.dts

       mdio-mux {
                compatible = "mdio-mux-gpio";
                pinctrl-0 = <&pinctrl_mdio_mux>;
                pinctrl-names = "default";
                gpios = <&gpio0 8  GPIO_ACTIVE_HIGH
                         &gpio0 9  GPIO_ACTIVE_HIGH
                         &gpio0 24 GPIO_ACTIVE_HIGH
                         &gpio0 25 GPIO_ACTIVE_HIGH>;
                mdio-parent-bus = <&mdio1>;
                #address-cells = <1>;
                #size-cells = <0>;


We have an MDIO multiplexor


                mdio_mux_1: mdio@1 {
                        reg = <1>;
                        #address-cells = <1>;
                        #size-cells = <0>;

                        switch0: switch@0 {
                                compatible = "marvell,mv88e6085";
                                pinctrl-0 = <&pinctrl_gpio_switch0>;
                                pinctrl-names = "default";
                                reg = <0>;
                                dsa,member = <0 0>;
                                interrupt-parent = <&gpio0>;
                                interrupts = <27 IRQ_TYPE_LEVEL_LOW>;

On the first bus, we have a Ethernet switch.

                                interrupt-controller;
                                #interrupt-cells = <2>;
                                eeprom-length = <512>;

                                ports {
                                        #address-cells = <1>;
                                        #size-cells = <0>;

                                        port@0 {
                                                reg = <0>;
                                                label = "lan0";
                                                phy-handle = <&switch0phy0>;
                                        };

The first port of that switch has a pointer to a PHY.

                               mdio {
                                        #address-cells = <1>;
                                        #size-cells = <0>;

That Ethernet switch also has an MDIO bus,

                                        switch0phy0: switch0phy0@0 {
                                                reg = <0>;

On that bus is the PHY.

                                                interrupt-parent = <&switch0>;
                                                interrupts = <0 IRQ_TYPE_LEVEL_HIGH>;

And that PHY has an interrupt. And that interrupt is provided by the switch.

Given your description, it sounds like this is also go to break.

vf610-zii-dev-rev-c.dts is the same pattern, and there are more
examples for mv88e6xxx.

It is a common pattern, e.g. the mips ar9331.dtsi follows it.

I've not yet looked at plain Ethernet drivers. This pattern could also
exist there. And i wonder about other complex structures, i2c bus
multiplexors, you can have interrupt controllers as i2c devices,
etc. So the general case could exist in other places.

I don't think we should be playing whack-a-mole by changing drivers as
we find they regress and break. We need a generic fix. I think the
solution is pretty clear. As you said the device depends on its
parent. DT is a tree, so it is easy to walk up the tree to detect this
relationship, and not fail the probe.

   Andrew

  reply	other threads:[~2021-08-27 13:44 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26  7:45 [PATCH v1 0/2] Fix rtl8366rb issues with fw_devlink=on Saravana Kannan
2021-08-26  7:45 ` [PATCH v1 1/2] driver core: fw_devlink: Add support for FWNODE_FLAG_BROKEN_PARENT Saravana Kannan
2021-08-26 13:13   ` Andrew Lunn
2021-08-26 19:56     ` Saravana Kannan
2021-08-26 20:53       ` Andrew Lunn
2021-08-26 23:44         ` Saravana Kannan
2021-08-27  1:23           ` Andrew Lunn
2021-08-27  4:02             ` Saravana Kannan
2021-08-27 13:44               ` Andrew Lunn [this message]
2021-08-27 18:06                 ` Saravana Kannan
2021-08-27 20:11                   ` Andrew Lunn
2021-08-27 21:33                     ` Saravana Kannan
2021-08-28 17:01                       ` Andrew Lunn
2021-08-30 19:03                         ` Saravana Kannan
2021-08-31 13:16                           ` Andrew Lunn
2021-08-31 19:26                             ` Saravana Kannan
2021-08-31 22:05                               ` Andrew Lunn
2021-08-31 22:18                                 ` Saravana Kannan
2021-08-31 23:02                                   ` Andrew Lunn
2021-08-31 23:18                                     ` Vladimir Oltean
2021-08-31 23:27                                       ` Andrew Lunn
2021-09-01  1:28                                       ` Vladimir Oltean
2021-09-01  1:38                                         ` Vladimir Oltean
2021-09-01  2:19                                           ` Saravana Kannan
2021-09-01  9:02                                             ` Vladimir Oltean
2021-09-01 22:57                                               ` Saravana Kannan
2021-09-01  2:00                                       ` Saravana Kannan
2021-09-01  8:46                                         ` Vladimir Oltean
2021-09-01 22:53                                           ` Saravana Kannan
2021-09-02 17:41                                           ` Andrew Lunn
2021-09-02 17:58                                             ` Saravana Kannan
2021-09-30  5:33                                       ` Saravana Kannan
2021-09-30 13:15                                         ` Andrew Lunn
2021-09-30 13:43                                         ` Vladimir Oltean
2021-09-30 14:00                                           ` Andrew Lunn
2021-09-30 17:31                                             ` Saravana Kannan
2021-09-30 19:38                                               ` Andrew Lunn
2021-09-30 19:48                                                 ` Saravana Kannan
2021-09-30 20:06                                                   ` Florian Fainelli
2021-09-30 20:14                                                     ` Saravana Kannan
2021-09-30 21:16                                                       ` Florian Fainelli
2021-09-30 20:22                                                     ` Andrew Lunn
2021-09-01  1:46                                     ` Saravana Kannan
2021-08-31 23:18                                   ` Andrew Lunn
2021-09-08 18:35                             ` Saravana Kannan
2021-09-09  1:39                           ` Andrew Lunn
2021-09-09  3:21                             ` Saravana Kannan
2021-09-09 10:38                               ` Vladimir Oltean
2021-09-09 15:00                               ` Andrew Lunn
2021-09-09 16:56                             ` Florian Fainelli
2021-08-26  7:45 ` [PATCH v1 2/2] net: dsa: rtl8366rb: Quick fix to work with fw_devlink=on Saravana Kannan
2021-08-26  7:55   ` Greg Kroah-Hartman
2021-08-26 11:25   ` Florian Fainelli
2021-08-26 17:29     ` Saravana Kannan
2021-08-26 11:29   ` Alvin Šipraga
2021-08-26 17:26     ` Saravana Kannan
2021-08-26 18:04       ` Alvin Šipraga

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