i2c: mv64xxx: Set bus frequency to 100kHz if clock-frequency is not provided

This commit adds checking whether clock-frequency property acquisition
has succeeded. If not, the frequency is set to 100kHz by default.

The Device Tree binding documentation is updated accordingly.

Based on the intials patches from Zbigniew Bodek
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Zbigniew Bodek <zbb@semihalf.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/devicetree/bindings/i2c/i2c-mv64xxx.txt

@@ -6,7 +6,11 @@ Required properties :
  - reg             : Offset and length of the register set for the device
  - compatible      : Should be "marvell,mv64xxx-i2c"
  - interrupts      : The interrupt number
- - clock-frequency : Desired I2C bus clock frequency in Hz.
+
+Optional properties :
+
+ - clock-frequency : Desired I2C bus clock frequency in Hz. If not set the
+default frequency is 100kHz
 
 Examples:
 

drivers/i2c/busses/i2c-mv64xxx.c

@@ -578,7 +578,11 @@ mv64xxx_of_config(struct mv64xxx_i2c_data *drv_data,
 		goto out;
 	}
 	tclk = clk_get_rate(drv_data->clk);
-	of_property_read_u32(np, "clock-frequency", &bus_freq);
+
+	rc = of_property_read_u32(np, "clock-frequency", &bus_freq);
+	if (rc)
+		bus_freq = 100000; /* 100kHz by default */
+
 	if (!mv64xxx_find_baud_factors(bus_freq, tclk,
 				       &drv_data->freq_n, &drv_data->freq_m)) {
 		rc = -EINVAL;