Re: MDIO over I2C driver driver probe dependency issue
From: Florian Fainelli <f.fainelli@gmail.com>
Date: 2021-01-08 03:06:17
On 1/7/2021 6:22 PM, Brian Silverman wrote:
I've written a very small generic MDIO driver that uses the existing mdio-i2c.c library in drivers/net/phy. The driver allows communication to the PHY's MDIO interface as using I2C, as supported by PHYs like the BCM54616S. This is working on my hardware. The one issue I have is that I2C is not up and available (i.e. probed) at the time that the MDIO interface comes up. To fix this, I've changed the device order in drivers/Makefile to put "obj-y += i2c/" before "obj-y += net/". While that works, I prefer not to have to keep that difference from mainline Linux. Also, I don't understand why i2c drivers occur arbitrarily late in the Makefile - surely there are other devices drivers that need i2c to be enabled when they are probed? Is there a way to do this that doesn't change probe order? Or is there a way to change probe order without patching mainline Linux?
Linux supports probe deferral so when a consumer of a resource finds that said resource's provider is not available, it should return -EPROBE_DEFER which puts the driver's probe routine onto a list of driver's probe function to retry at a later time. In your case the GEM Ethernet driver should get an -EPROBE_DEFER while the Ethernet PHY device tree node is looked up via phylink_of_phy_connect() because the mdio-i2c-gen i2c client has not had a chance to register the MDIO bus yet. Have you figured out the call path that does not work for you? Which version of the kernel are you using? What I am referring to is assuming mainline, but maybe this is not your case?
---
For reference, here's the driver (excluding headers and footers):
static int mdio_i2c_gen_probe(struct i2c_client *client,
const struct i2c_device_id *id)
{
struct mii_bus *bus;
bus = mdio_i2c_alloc(&client->dev, client->adapter);
if (IS_ERR(bus)){
return PTR_ERR(bus);
}
bus->name = "Generic MDIO bus over I2C";
bus->parent = &client->dev;
return of_mdiobus_register(bus, client->dev.of_node);
}
static int mdio_i2c_gen_remove(struct i2c_client *client)
{
return 0;
}
static const struct of_device_id mdio_i2c_gen_of_match[] = {
{ .compatible = "mdio-i2c-gen", },
{ }
};
MODULE_DEVICE_TABLE(of, mdio_i2c_gen_of_match);
static struct i2c_driver mdio_i2c_gen_driver = {
.driver = {
.name= "mdio-i2c-gen",
.of_match_table = of_match_ptr(mdio_i2c_gen_of_match),
},
.probe= mdio_i2c_gen_probe,
.remove= mdio_i2c_gen_remove,
};
module_i2c_driver(mdio_i2c_gen_driver);
---
And here's a device-tree snippet:
&gem3 {
status = "okay";
phy-handle = <&phy0>;
};
&i2c0 {
mdio@40 {
compatible = "mdio-i2c-gen";
reg = <0x40>;
#address-cells = <1>;
#size-cells = <0>;
phy0: phy@0 {
reg = <0>;
};
};
};
-- Florian