linux-kernel - [PATCH v3 1/1] i2c: core: support no-detect property

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Date:   Fri, 29 Apr 2022 15:07:49 +0200
From:   Vincent Whitchurch <vincent.whitchurch@...s.com>
To:     <wsa@...nel.org>
CC:     <kernel@...s.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        <linux-i2c@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v3 1/1] i2c: core: support no-detect property

If the devicetree specifies the no-detect property (documented in
dt-schema [0]) for the I2C bus, we know that there are no other devices
on the bus other than the ones listed in the devicetree, so avoid
calling drivers' detect callbacks and wasting time looking for devices
which do not exist.

[0] https://github.com/devicetree-org/dt-schema/commit/ba55f96c6d8d

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@...s.com>
---
 drivers/i2c/i2c-core-base.c | 8 +++++++-
 include/linux/i2c.h         | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index d43db2c3876e..d43025b84546 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1341,7 +1341,8 @@ static int i2c_do_add_adapter(struct i2c_driver *driver,
 			      struct i2c_adapter *adap)
 {
 	/* Detect supported devices on that bus, and instantiate them */
-	i2c_detect(adap, driver);
+	if (adap->detect)
+		i2c_detect(adap, driver);
 
 	return 0;
 }
@@ -1432,6 +1433,7 @@ EXPORT_SYMBOL_GPL(i2c_handle_smbus_host_notify);
 
 static int i2c_register_adapter(struct i2c_adapter *adap)
 {
+	struct device_node *np = adap->dev.of_node;
 	int res = -EINVAL;
 
 	/* Can't register until after driver model init */
@@ -1502,6 +1504,10 @@ static int i2c_register_adapter(struct i2c_adapter *adap)
 			 "Failed to create compatibility class link\n");
 #endif
 
+	adap->detect = true;
+	if (np && of_property_read_bool(np, "no-detect"))
+		adap->detect = false;
+
 	/* create pre-declared device nodes */
 	of_i2c_register_devices(adap);
 	i2c_acpi_install_space_handler(adap);
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index fbda5ada2afc..8fad5fe85685 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -728,6 +728,7 @@ struct i2c_adapter {
 	struct rt_mutex bus_lock;
 	struct rt_mutex mux_lock;
 
+	bool detect;
 	int timeout;			/* in jiffies */
 	int retries;
 	struct device dev;		/* the adapter device */
-- 
2.34.1