[PATCH v3 1/7] i2c: mux: add the ability to share mux address with child nodes

[Farouk Bouabid]

Allow the mux (if it's an I2C device) to have the same address as a child
device. This is useful when the mux can only use an I2C address that is
used by a child device because no other addresses are free to use.
eg. the mux can only use address 0x18 which is used by amc6821 connected
to the mux.

Signed-off-by: Farouk Bouabid <farouk.bouabid at cherry.de>
---
 drivers/i2c/i2c-core-base.c |  6 +++++-
 drivers/i2c/i2c-mux.c       | 48 ++++++++++++++++++++++++++++++++++++++++++++-
 include/linux/i2c-mux.h     |  1 +
 include/linux/i2c.h         |  7 +++++++
 4 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index ff5c486a1dbb..ce2425b0486d 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -821,9 +821,13 @@ static int i2c_check_mux_children(struct device *dev, void *addrp)
 static int i2c_check_addr_busy(struct i2c_adapter *adapter, int addr)
 {
 	struct i2c_adapter *parent = i2c_parent_is_i2c_adapter(adapter);
+	bool skip_check = false;
 	int result = 0;
 
-	if (parent)
+	if (adapter->quirks && adapter->quirks->flags & I2C_AQ_SKIP_ADDR_CHECK)
+		skip_check = adapter->quirks->skip_addr_in_parent == addr;
+
+	if (parent && !skip_check)
 		result = i2c_check_mux_parents(parent, addr);
 
 	if (!result)
diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 57ff09f18c37..644509bc3496 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -334,7 +334,53 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 	priv->adap.dev.parent = &parent->dev;
 	priv->adap.retries = parent->retries;
 	priv->adap.timeout = parent->timeout;
-	priv->adap.quirks = parent->quirks;
+
+	struct i2c_adapter_quirks *quirks;
+	/*
+	 * When creating the adapter, the node devices are checked for I2C address
+	 * match with other devices on the parent adapter, among which is the mux itself.
+	 * If a match is found the node device is not probed successfully.
+	 * Allow the mux to have the same address as a child device by skipping this check.
+	 */
+	if (muxc->share_addr_with_children) {
+		struct i2c_client *client = to_i2c_client(muxc->dev);
+
+		if (muxc->dev->type != &i2c_client_type)
+			dev_warn_once(muxc->dev, "Mux is not an I2C device\n");
+
+		quirks = devm_kzalloc(muxc->dev, sizeof(*quirks), GFP_KERNEL);
+		if (!quirks)
+			return -ENOMEM;
+
+		if (parent->quirks)
+			memcpy(quirks, parent->quirks, sizeof(*quirks));
+
+		quirks->flags |= I2C_AQ_SKIP_ADDR_CHECK;
+		quirks->skip_addr_in_parent = client->addr;
+		priv->adap.quirks = quirks;
+
+	} else if (parent->quirks &&
+		   parent->quirks->flags & I2C_AQ_SKIP_ADDR_CHECK) {
+		/*
+		 * Another I2C mux device can be a child of the Mule I2C mux.
+		 * The former could probably not allow address conflict between
+		 * its address and its own children addresses.
+		 *
+		 * For this purpose, do not propagate this flag unless
+		 * share_addr_with_children is set.
+		 */
+		quirks = devm_kzalloc(muxc->dev, sizeof(*quirks), GFP_KERNEL);
+		if (!quirks)
+			return -ENOMEM;
+
+		memcpy(quirks, parent->quirks, sizeof(*quirks));
+		quirks->flags &= ~I2C_AQ_SKIP_ADDR_CHECK;
+		priv->adap.quirks = quirks;
+
+	} else {
+		priv->adap.quirks = parent->quirks;
+	}
+
 	if (muxc->mux_locked)
 		priv->adap.lock_ops = &i2c_mux_lock_ops;
 	else
diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
index 98ef73b7c8fd..17ac68bf1703 100644
--- a/include/linux/i2c-mux.h
+++ b/include/linux/i2c-mux.h
@@ -21,6 +21,7 @@ struct i2c_mux_core {
 	unsigned int mux_locked:1;
 	unsigned int arbitrator:1;
 	unsigned int gate:1;
+	unsigned int share_addr_with_children:1;
 
 	void *priv;
 
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 5e6cd43a6dbd..c3acbaaadae9 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -670,6 +670,7 @@ int i2c_generic_scl_recovery(struct i2c_adapter *adap);
  * @max_read_len: maximum length of a read message
  * @max_comb_1st_msg_len: maximum length of the first msg in a combined message
  * @max_comb_2nd_msg_len: maximum length of the second msg in a combined message
+ * @skip_addr_in_parent: No conflict check on parent adapter for a given address
  *
  * Note about combined messages: Some I2C controllers can only send one message
  * per transfer, plus something called combined message or write-then-read.
@@ -690,6 +691,7 @@ struct i2c_adapter_quirks {
 	u16 max_read_len;
 	u16 max_comb_1st_msg_len;
 	u16 max_comb_2nd_msg_len;
+	unsigned short skip_addr_in_parent;
 };
 
 /* enforce max_num_msgs = 2 and use max_comb_*_len for length checks */
@@ -711,6 +713,11 @@ struct i2c_adapter_quirks {
 #define I2C_AQ_NO_ZERO_LEN		(I2C_AQ_NO_ZERO_LEN_READ | I2C_AQ_NO_ZERO_LEN_WRITE)
 /* adapter cannot do repeated START */
 #define I2C_AQ_NO_REP_START		BIT(7)
+/**
+ * do not check for conflict on a given address
+ * used accordingly with "struct i2c_adapter_quirks.skip_addr_in_parent"
+ */
+#define I2C_AQ_SKIP_ADDR_CHECK	BIT(8)
 
 /*
  * i2c_adapter is the structure used to identify a physical i2c bus along

-- 
2.34.1