[PATCH v7 0/3] lan966x pci device: Add support for SFPs, i2c part

[PATCH v7 0/3] lan966x pci device: Add support for SFPs, i2c part

[Herve Codina]

Hi,

Previously, I sent a big picture series adding support for SFP ports
available on the LAN966x PCI device [0].

In this series patches touch several parts and sub-system in the kernel.
Reviews have be done and it makes sense to split the series and send
parts separately.

This current series is the extraction of patches related to issues in
the I2C subsystem. It has to be seen as a continuation of the big
picture series but related to this specific I2C part.

Those patches are related fw_delink issues specific to I2C muxes.

They purpose is to correctly set a link between an adapter supplier and
its consumer. Indeed, an i2c mux adapter's parent is not the i2c mux
supplier but the adapter the i2c mux is connected to. Adding a new link
between the adapter supplier involved when i2c muxes are used avoid a
freeze observed during device removal.

[0] https://lore.kernel.org/all/20260325143555.451852-1-herve.codina@bootlin.com/

Best regards,
Hervé

Changes:

v6 -> v7

  Rebase on top v7.1-rc1

  - Patch 1, 2 and 3
    No changes

Older iterations:
  Patches 14, 15 and 16in the big picture series
  https://lore.kernel.org/all/20260325143555.451852-1-herve.codina@bootlin.com/

Herve Codina (3):
  i2c: core: Introduce i2c_get_adapter_physdev()
  i2c: mux: Set adapter physical device
  i2c: mux: Create missing devlink between mux and adapter physical
    device

 drivers/i2c/i2c-core-base.c | 16 ++++++++++++++++
 drivers/i2c/i2c-mux.c       | 26 ++++++++++++++++++++++++++
 include/linux/i2c.h         |  3 +++
 3 files changed, 45 insertions(+)

-- 
2.54.0

[PATCH v7 1/3] i2c: core: Introduce i2c_get_adapter_physdev()

[Herve Codina]

The physical device providing an I2C adapter is the device that calls
i2c_add_adapter() or variants and i2c_del_adapter().

Most of the time this physical device is the parent of the adapter
device.

Exceptions exist with i2c muxes. Indeed, in case of i2c muxes, the
parent of the mux adapter device points to the adapter device the mux is
connected to instead of the physical of this mux adapter.

Introduce i2c_get_adapter_physdev() and a new physdev field in the
adapter structure in order to ease the adapter physical device
retrieval.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
---
 drivers/i2c/i2c-core-base.c | 16 ++++++++++++++++
 include/linux/i2c.h         |  3 +++
 2 files changed, 19 insertions(+)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index 9c46147e3506..59214f0c84ec 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1919,6 +1919,22 @@ struct i2c_adapter *i2c_get_adapter_by_fwnode(struct fwnode_handle *fwnode)
 }
 EXPORT_SYMBOL(i2c_get_adapter_by_fwnode);
 
+/**
+ * i2c_get_adapter_physdev() - Get the physical device of an adapter
+ * @adapter: the adapter to get the physical device from
+ *
+ * Return:
+ * Look up and return the &struct device corresponding to the device supplying
+ * this @adapter.
+ *
+ * The user must call put_device() once done with the physical device returned.
+ */
+struct device *i2c_get_adapter_physdev(struct i2c_adapter *adapter)
+{
+	return get_device(adapter->physdev ?: adapter->dev.parent);
+}
+EXPORT_SYMBOL(i2c_get_adapter_physdev);
+
 static void i2c_parse_timing(struct device *dev, char *prop_name, u32 *cur_val_p,
 			    u32 def_val, bool use_def)
 {
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 20fd41b51d5c..dff04d20cafe 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -744,6 +744,7 @@ struct i2c_adapter {
 	int timeout;			/* in jiffies */
 	int retries;
 	struct device dev;		/* the adapter device */
+	struct device *physdev;		/* the physical device */
 	unsigned long locked_flags;	/* owned by the I2C core */
 #define I2C_ALF_IS_SUSPENDED		0
 #define I2C_ALF_SUSPEND_REPORTED	1
@@ -911,6 +912,8 @@ struct i2c_adapter *i2c_get_adapter(int nr);
 void i2c_put_adapter(struct i2c_adapter *adap);
 unsigned int i2c_adapter_depth(struct i2c_adapter *adapter);
 
+struct device *i2c_get_adapter_physdev(struct i2c_adapter *adap);
+
 void i2c_parse_fw_timings(struct device *dev, struct i2c_timings *t, bool use_defaults);
 
 /* Return the functionality mask */
-- 
2.54.0

[PATCH v7 2/3] i2c: mux: Set adapter physical device

[Herve Codina]

For i2c muxes, the parent of the mux adapter device is the adapter
device the mux is connected to.

This parent is not the physical device related to the mux adapter.
Indeed, the physical device of the mux adapter is the mux device itself.

Fill the adap.physdev with the mux device.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
---
 drivers/i2c/i2c-mux.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 681a201c239b..f4e73e7a0e33 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -315,6 +315,7 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 	priv->adap.algo = &priv->algo;
 	priv->adap.algo_data = priv;
 	priv->adap.dev.parent = &parent->dev;
+	priv->adap.physdev = muxc->dev;
 	priv->adap.retries = parent->retries;
 	priv->adap.timeout = parent->timeout;
 	priv->adap.quirks = parent->quirks;
-- 
2.54.0

[PATCH v7 3/3] i2c: mux: Create missing devlink between mux and adapter physical device

[Herve Codina]

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 downstream 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.

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

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index f4e73e7a0e33..26470a7c2eea 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -268,7 +268,9 @@ 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;
 
@@ -375,6 +377,29 @@ 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);
-- 
2.54.0