Re: [PATCH v2 16/26] i2c: mux: Create missing devlink between mux and adapter physical device

Andy Shevchenko
2025-05-08T19:15:45Z

On Wed, May 07, 2025 at 09:12:58AM +0200, Herve Codina wrote:
> When removing an i2c controller device handling an i2c bus where an i2c
> mux is connected to, the removal process hangs and is stuck in the
> wait_completion() call done in i2c_del_adapter().
>
> The i2c_del_adapter() tries to removed the i2c adapter related to the
> i2c controller device and the wait_completion() is waiting for the i2c
> adapter device release. This release is performed when the device is no
> more used (i.e. refcount reaches zero).
>
> When an i2c mux is involved in an i2c path, the struct dev topology is
> the following:
> +----------------+ +-------------------+
> | i2c controller | | i2c mux |
> | device | | device |
> | ^ | | |
> | | | | |
> | dev's parent | | |
> | | | | |
> | i2c adapter | | i2c adapter chanX |
> | device <---- dev's parent ------ device |
> | (no driver) | | (no driver) |
> +----------------+ +-------------------+
>
> When an i2c mux device creates an i2c adapter for its downstream
> channel, a reference is taken to its adapter dev's parent. This parent
> is the i2c mux upstream adapter device.
>
> No relationship exists between the i2c mux device itself and the i2c
> controller device (physical device) in order to have the i2c mux device
> calling i2c_del_adapter() to remove its downtream adapters and so,
> release references taken to the upstream adapter.
>
> This consumer/supplier relationship is typically a devlink relationship.
>
> Also, i2c muxes can be chained and so, the upstream adapter can be
> supplied by either an i2c controller device or an other i2c mux device.
>
> In order to get the physical device of the adapter a mux is connected
> to, rely on the newly introduced i2c_adapter_get_physdev() and create
> the missing devlink between the i2c mux device and the physical
> device of the adapter the mux is connected to.
>
> With that done, the i2c mux device is removed before the device
> handling the upstream i2c adapter (i2c controller device or i2c mux
> device). All references are released and the i2c_del_adapter() call
> performed by driver handling the upstream adapter device is not blocking
> anymore.

...

> + /*
> + * There is no relationship set between the mux device and the physical
> + * device handling the parent adapter. Create this missing relationship
> + * in order to remove the i2c mux device (consumer) and so the dowstream
> + * channel adapters before removing the physical device (supplier) which
> + * handles the i2c mux upstream adapter.
> + */
> + parent_physdev = i2c_get_adapter_physdev(parent);
> + dl = device_link_add(muxc->dev, parent_physdev, DL_FLAG_AUTOREMOVE_CONSUMER);
> + if (!dl) {
> + dev_err(muxc->dev, "failed to create device link to %s\n",
> + dev_name(parent_physdev));
> + put_device(parent_physdev);
> + ret = -EINVAL;
> + goto err_free_priv;
> + }
> + put_device(parent_physdev);

Since you are not checking parent_physdev for NULL, the dev_name() can print a
"(null)" string. Is this by design?

--
With Best Regards,
Andy Shevchenko