linux-kernel - [PATCH v2 2/2] i2c: core: support no-detect property

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Date:   Tue, 12 Apr 2022 10:50:46 +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>,
        <krzk+dt@...nel.org>, <robh+dt@...nel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH v2 2/2] i2c: core: support no-detect property

If the devicetree specifies the no-detect property, we know that there
are no other devices on the bus other than the ones listed in the
devicetree, so avoid calling drivers' detect callback and wasting time
probing for devices which do not exist.

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