[PATCH v2] i2c: core: helper function to detect slave mode

[Luis Oliveira]

This function has the purpose of mode detection by checking the
device nodes for a reg matching with the I2C_OWN_SLAVE_ADDREESS flag.
Currently only checks using OF functions (ACPI slave not supported yet).

Signed-off-by: Luis Oliveira <loli...@synopsys.com>
Suggested-by: Andy Shevchenko <andy.shevche...@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevche...@gmail.com>
---
Changes V1->V2:
- Kernel doc added to i2c-core. (@Andy)
- Moved the definitions to the OF branch. (@Andy)
- Changed the return type from int to bool. (@Rob)

 drivers/i2c/i2c-core.c | 28 ++++++++++++++++++++++++++++
 include/linux/i2c.h    |  1 +
 2 files changed, 29 insertions(+)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 3de95a29024c..937605e65976 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -3691,6 +3691,34 @@ int i2c_slave_unregister(struct i2c_client *client)
        return ret;
 }
 EXPORT_SYMBOL_GPL(i2c_slave_unregister);
+
+/**
+ * i2c_slave_mode_detect - detect operation mode
+ * @dev:  The device owning the bus
+ *
+ * This checks the device nodes for a I2C slave by checking the address
+ * used.
+ *
+ * Returns true if a I2C slave is detected, otherwise returns false.
+ */
+bool i2c_slave_mode_detect(struct device *dev)
+{
+       if (IS_BUILTIN(CONFIG_OF) && dev->of_node) {
+               struct device_node *child;
+               u32 reg;
+
+               for_each_child_of_node(dev->of_node, child) {
+                       of_property_read_u32(child, "reg", &reg);
+                       if (reg & I2C_OWN_SLAVE_ADDRESS)
+                               return true;
+               }
+       } else if (IS_BUILTIN(CONFIG_ACPI) && ACPI_HANDLE(dev)) {
+               dev_dbg(dev, "ACPI slave is not supported yet\n");
+       }
+       return false;
+}
+EXPORT_SYMBOL_GPL(i2c_slave_mode_detect);
+
 #endif
 
 MODULE_AUTHOR("Simon G. Vogl <si...@tk.uni-linz.ac.at>");
diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index b2109c522dec..bfc3e0cee57e 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -282,6 +282,7 @@ enum i2c_slave_event {
 
 extern int i2c_slave_register(struct i2c_client *client, i2c_slave_cb_t 
slave_cb);
 extern int i2c_slave_unregister(struct i2c_client *client);
+extern bool i2c_slave_mode_detect(struct device *dev);
 
 static inline int i2c_slave_event(struct i2c_client *client,
                                  enum i2c_slave_event event, u8 *val)
-- 
2.11.0