[PATCH v9 3/3] i2c: {mux,atr}: Create missing devlink between mux/atr and adapter physical device

[Herve Codina <herve.codina@bootlin.com>]

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 (and/or atr) is involved in an i2c path, the struct dev
topology is the following:

    +----------------+                +-------------------+
    | i2c controller |                |    i2c mux/atr    |
    |     device     |                |      device       |
    |       ^        |                |                   |
    |       |        |                |                   |
    |  dev's parent  |                |                   |
    |       |        |                |                   |
    |   i2c adapter  |                | i2c adapter chanX |
    |     device  <---- dev's parent ------  device       |
    |   (no driver)  |                |    (no driver)    |
    +----------------+                +-------------------+

When an i2c mux/atr 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/atr upstream adapter device.

No relationship exists between the i2c mux/atr device itself and the i2c
controller device (physical device) in order to have the i2c mux/atr
device calling i2c_del_adapter() to remove its downstream adapters and so,
release references taken to the upstream adapter.

This consumer/supplier relationship is typically a devlink relationship.

Also, i2c muxes/atrs can be chained and so, the upstream adapter can be
supplied by either an i2c controller device or an other i2c mux/atr
device.

In order to get the physical device of the adapter a mux/atr is
connected to, rely on the newly introduced i2c_adapter_get_physdev() and
create the missing devlink between the i2c mux/atr device and the
physical device of the adapter the mux/atr is connected to.

With that done, the i2c mux/atr device is removed before the device
handling the upstream i2c adapter (i2c controller device or i2c mux/atr
device). All references are released and the i2c_del_adapter() call
performed by driver handling the upstream adapter device is not blocking
anymore.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
 drivers/i2c/i2c-atr.c | 25 +++++++++++++++++++++++++
 drivers/i2c/i2c-mux.c | 25 +++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/drivers/i2c/i2c-atr.c b/drivers/i2c/i2c-atr.c
index a591d39050e7..94ff543d4f8e 100644
--- a/drivers/i2c/i2c-atr.c
+++ b/drivers/i2c/i2c-atr.c
@@ -788,9 +788,11 @@ int i2c_atr_add_adapter(struct i2c_atr *atr, struct i2c_atr_adap_desc *desc)
 	struct fwnode_handle *bus_handle = desc->bus_handle;
 	struct i2c_adapter *parent = atr->parent;
 	char symlink_name[ATR_MAX_SYMLINK_LEN];
+	struct device *parent_physdev;
 	struct device *dev = atr->dev;
 	u32 chan_id = desc->chan_id;
 	struct i2c_atr_chan *chan;
+	struct device_link *dl;
 	int ret, idx;
 
 	if (chan_id >= atr->max_adapters) {
@@ -866,6 +868,29 @@ int i2c_atr_add_adapter(struct i2c_atr *atr, struct i2c_atr_adap_desc *desc)
 
 	atr->adapter[chan_id] = &chan->adap;
 
+	/*
+	 * There is no relationship set between the atr device and the physical
+	 * device handling the parent adapter. Create this missing relationship
+	 * in order to remove the i2c atr device (consumer) and so the dowstream
+	 * channel adapters before removing the physical device (supplier) which
+	 * handles the i2c atr upstream adapter.
+	 */
+	parent_physdev = i2c_get_adapter_physdev(parent);
+	if (!parent_physdev) {
+		dev_err(dev, "failed to get the parent physical device\n");
+		ret = -ENODEV;
+		goto err_free_alias_pool;
+	}
+	dl = device_link_add(dev, parent_physdev, DL_FLAG_AUTOREMOVE_CONSUMER);
+	if (!dl) {
+		dev_err(dev, "failed to create device link to %s\n",
+			dev_name(parent_physdev));
+		put_device(parent_physdev);
+		ret = -EINVAL;
+		goto err_free_alias_pool;
+	}
+	put_device(parent_physdev);
+
 	ret = i2c_add_adapter(&chan->adap);
 	if (ret) {
 		atr->adapter[chan_id] = NULL;
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index c1836114ef56..0cfb581b4ef1 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -314,7 +314,9 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 			u32 force_nr, u32 chan_id)
 {
 	struct i2c_adapter *parent = muxc->parent;
+	struct device *parent_physdev;
 	struct i2c_mux_priv *priv;
+	struct device_link *dl;
 	char symlink_name[20];
 	int ret;
 
@@ -382,6 +384,29 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 				      ACPI_COMPANION(muxc->dev),
 				      chan_id);
 
+	/*
+	 * 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);
+	if (!parent_physdev) {
+		dev_err(muxc->dev, "failed to get the parent physical device\n");
+		ret = -ENODEV;
+		goto err_free_priv;
+	}
+	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);
+
 	if (force_nr) {
 		priv->adap.nr = force_nr;
 		ret = i2c_add_numbered_adapter(&priv->adap);
-- 
2.56.0