On Wed, Feb 10, 2021 at 2:52 PM Andrew Lunn <and...@lunn.ch> wrote: > > On Wed, Feb 10, 2021 at 02:13:48PM -0800, Saravana Kannan wrote: > > Hi, > > > > This email was triggered by this other email[1]. > > > > Why is phy_attach_direct() directly calling device_bind_driver() > > instead of using bus_probe_device()? > > Hi Saravana > > So this is to do with the generic PHY, which is a special case. > > First the normal case. The MDIO bus driver registers an MDIO bus using > mdiobus_register(). This will enumerate the bus, finding PHYs on > it. Each PHY device is registered with the device core, using the > usual device_add(). The core will go through the registered PHY > drivers and see if one can drive this hardware, based on the ID > registers the PHY has at address 2 and 3. If a match is found, the > driver probes the device, all in the usual way. > > Sometime later, the MAC driver wants to make use of the PHY > device. This is often in the open() call of the MAC driver, when the > interface is configured up. The MAC driver asks phylib to associate a > PHY devices to the MAC device. In the normal case, the PHY has been > probed, and everything is good to go. > > However, sometimes, there is no driver for the PHY. There is no driver > for that hardware. Or the driver has not been built, or it is not on > the disk, etc. So the device core has not been able to probe > it. However, IEEE 802.3 clause 22 defines a minimum set of registers a > PHY should support. And most PHY devices have this minimum. So there > is a fall back driver, the generic PHY driver. It assumes the minimum > registers are available, and does its best to drive the hardware. It > often works, but not always. So if the MAC asks phylib to connect to a > PHY which does not have a driver, we forcefully bind the generic > driver to the device, and hope for the best.
Thanks for the detailed answer Andrew! I think it gives me enough info/context to come up with a proper fix. > We don't actually recommend using the generic driver. Use the specific > driver for the hardware. But the generic driver can at least get you > going, allow you to scp the correct driver onto the system, etc. I'm not sure if I can control what driver they use. If I can fix this warning, I'll probably try to do that. -Saravana