i2c: core: add api to provide frequency mode strings

Some I2C drivers like Designware and HiSilicon will print the
bus frequency mode information, so add a public one that everyone
can make use of.

Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
index c4c28b5..5c16083 100644
--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -76,6 +76,27 @@ void i2c_transfer_trace_unreg(void)
 	static_branch_dec(&i2c_trace_msg_key);
 }
 
+const char *i2c_freq_mode_string(u32 bus_freq_hz)
+{
+	switch (bus_freq_hz) {
+	case I2C_MAX_STANDARD_MODE_FREQ:
+		return "Standard Mode (100 kHz)";
+	case I2C_MAX_FAST_MODE_FREQ:
+		return "Fast Mode (400 kHz)";
+	case I2C_MAX_FAST_MODE_PLUS_FREQ:
+		return "Fast Mode Plus (1.0 MHz)";
+	case I2C_MAX_TURBO_MODE_FREQ:
+		return "Turbo Mode (1.4 MHz)";
+	case I2C_MAX_HIGH_SPEED_MODE_FREQ:
+		return "High Speed Mode (3.4 MHz)";
+	case I2C_MAX_ULTRA_FAST_MODE_FREQ:
+		return "Ultra Fast Mode (5.0 MHz)";
+	default:
+		return "Unknown Mode";
+	}
+}
+EXPORT_SYMBOL_GPL(i2c_freq_mode_string);
+
 const struct i2c_device_id *i2c_match_id(const struct i2c_device_id *id,
 						const struct i2c_client *client)
 {