Re: [PATCH v3 2/3] driver core: fw_devlink: Add support for FWNODE_FLAG_NEEDS_CHILD_BOUND_ON_ADD

On Tue, Sep 21, 2021 at 2:03 PM Andrew Lunn [off-list ref] wrote:

quoted

There are cases where the children try to probe too quickly (before
the parent has had time to set up all the resources it's setting up)
and the child defers the probe. Even Andrew had an example of that
with some ethernet driver where the deferred probe is attempted
multiple times wasting time and then it eventually succeeds.

And i prefer an occasional EPROBE_DEFER over a broken Ethernet switch,
which is the current state. I'm happy to see optimisations, but not at
the expense of breaking working stuff.

Right, but in that case, the long term solution should be to make
changes so we don't expect the child to be bound as soon as it's
added. Not disable the optimization. Agree?

quoted

Also, this assumption that the child will be bound successfully upon
addition forces the parent/child drivers to play initcall chicken

We have never had any initcall chicken problems. The switch drivers
all are standard mdio_module_driver, module_platform_driver,
module_i2c_driver, module_pci_driver. Nothing special here. Things
load in whatever order they load, and it all works out, maybe with an
EPROBE_DEFER cycle. Which is good, we get our error paths tested, and
sometimes find bugs that way.

My comment was a general comment about parent drives that expect the
child drivers to be bound on addition -- not specific to DSA.

But even in the DSA case, not playing initcall chicken means if you
change the order of driver registration, things should still work.
However, as it stands, if you register the switch driver before the
PHY drivers are registered, you are going to force bind the PHYs to
the generic driver.

-Saravana