[PATCH RFC 1/7] i2c: core: add callback to change bus frequency

[Marcus Folkesson <marcus.folkesson@gmail.com>]

All devices on the same I2C bus share the same clock line and the bus
frequency has therefor be chosen so that all attached devices are able
to tolarate that clock rate. IOW, the bus speed must be set for the
slowest attached device.

With I2C multiplexers/switches on the other hand, it would be possible
to have different "domains" that runs with different speeds.

Prepare for such a feature by provide an optional callback function to
change bus frequency.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
---
 include/linux/i2c.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/include/linux/i2c.h b/include/linux/i2c.h
index 20fd41b51d5c85ee1665395c07345faafd8e2fca..d147e388dbab27966beb4dfbf869928b429e082c 100644
--- a/include/linux/i2c.h
+++ b/include/linux/i2c.h
@@ -742,6 +742,8 @@ struct i2c_adapter {
 	struct rt_mutex mux_lock;
 
 	int timeout;			/* in jiffies */
+	int clock_hz;
+	int (*set_clk_freq)(struct i2c_adapter *adap, u32 clock_hz); /* Optional */
 	int retries;
 	struct device dev;		/* the adapter device */
 	unsigned long locked_flags;	/* owned by the I2C core */
@@ -835,6 +837,17 @@ i2c_unlock_bus(struct i2c_adapter *adapter, unsigned int flags)
 	adapter->lock_ops->unlock_bus(adapter, flags);
 }
 
+static inline int
+i2c_adapter_set_clk_freq(struct i2c_adapter *adapter, u32 clock_hz)
+{
+	int ret = -EOPNOTSUPP;
+
+	if (adapter->set_clk_freq)
+		ret = adapter->set_clk_freq(adapter, clock_hz);
+
+	return ret;
+}
+
 /**
  * i2c_mark_adapter_suspended - Report suspended state of the adapter to the core
  * @adap: Adapter to mark as suspended

-- 
2.50.1