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

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Date: Fri, 26 Apr 2024 18:49:32 +0200
From: Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
To: Wolfram Sang <wsa+renesas@...g-engineering.com>, 
 Peter Rosin <peda@...ntia.se>, Andi Shyti <andi.shyti@...nel.org>, 
 Rob Herring <robh@...nel.org>, 
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, 
 Conor Dooley <conor+dt@...nel.org>, 
 Quentin Schulz <quentin.schulz@...obroma-systems.com>, 
 Heiko Stuebner <heiko@...ech.de>
Cc: linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org, 
 devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-rockchip@...ts.infradead.org, 
 Farouk Bouabid <farouk.bouabid@...obroma-systems.com>
Subject: [PATCH 1/7] i2c: mux: add the ability to share mux-address with
 child nodes

Allow the mux 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@...obroma-systems.com>
---
 drivers/i2c/i2c-mux.c   | 10 +++++++++-
 include/linux/i2c-mux.h |  1 +
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
index 57ff09f18c37..f5357dff8cc5 100644
--- a/drivers/i2c/i2c-mux.c
+++ b/drivers/i2c/i2c-mux.c
@@ -331,7 +331,6 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 	priv->adap.owner = THIS_MODULE;
 	priv->adap.algo = &priv->algo;
 	priv->adap.algo_data = priv;
-	priv->adap.dev.parent = &parent->dev;
 	priv->adap.retries = parent->retries;
 	priv->adap.timeout = parent->timeout;
 	priv->adap.quirks = parent->quirks;
@@ -348,6 +347,15 @@ int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
 	else
 		priv->adap.class = class;
 
+	/*
+	 * 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))
+		priv->adap.dev.parent = &parent->dev;
+
 	/*
 	 * Try to populate the mux adapter's of_node, expands to
 	 * nothing if !CONFIG_OF.
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;
 

-- 
2.34.1