[PATCH v3] i2c:at91: Add device tree property to set clock-frequency

[mark.roszko@gmail.com (Marek Roszko)]

This adds the ability to set "clock-frequency" in the device tree for the at91
i2cbus following the naming of other i2c bus implementations. If the property
is not set,the clock frequency will default to the previously used define 
of 100KHz.

Signed-off-by: Marek Roszko <mark.roszko@gmail.com>
---
v3:		
		-changed bus_clk_rate to u32
v2:
        -fixed return code usage and check to not compare agaisnt less than zero

---
 Documentation/devicetree/bindings/i2c/i2c-at91.txt |    2 ++
 drivers/i2c/busses/i2c-at91.c                      |   10 ++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Documentation/devicetree/bindings/i2c/i2c-at91.txt b/Documentation/devicetree/bindings/i2c/i2c-at91.txt
index 4fade84..388f0a2 100644
--- a/Documentation/devicetree/bindings/i2c/i2c-at91.txt
+++ b/Documentation/devicetree/bindings/i2c/i2c-at91.txt
@@ -12,6 +12,7 @@ Required properties :
 - clocks: phandles to input clocks.
 
 Optional properties:
+- clock-frequency: Desired I2C bus frequency in Hz, otherwise defaults to 100000
 - Child nodes conforming to i2c bus binding
 
 Examples :
@@ -23,6 +24,7 @@ i2c0: i2c at fff84000 {
 	#address-cells = <1>;
 	#size-cells = <0>;
 	clocks = <&twi0_clk>;
+	clock-frequency = <400000>;
 
 	24c512 at 50 {
 		compatible = "24c512";
diff --git a/drivers/i2c/busses/i2c-at91.c b/drivers/i2c/busses/i2c-at91.c
index 843d012..334c851 100644
--- a/drivers/i2c/busses/i2c-at91.c
+++ b/drivers/i2c/busses/i2c-at91.c
@@ -32,7 +32,7 @@
 #include <linux/slab.h>
 #include <linux/platform_data/dma-atmel.h>
 
-#define TWI_CLK_HZ		100000			/* max 400 Kbits/s */
+#define DEFAULT_TWI_CLK_HZ		100000		/* max 400 Kbits/s */
 #define AT91_I2C_TIMEOUT	msecs_to_jiffies(100)	/* transfer timeout */
 #define AT91_I2C_DMA_THRESHOLD	8			/* enable DMA if transfer size is bigger than this threshold */
 
@@ -711,6 +711,7 @@ static int at91_twi_probe(struct platform_device *pdev)
 	struct resource *mem;
 	int rc;
 	u32 phy_addr;
+	u32 bus_clk_rate;
 
 	dev = devm_kzalloc(&pdev->dev, sizeof(*dev), GFP_KERNEL);
 	if (!dev)
@@ -756,7 +757,12 @@ static int at91_twi_probe(struct platform_device *pdev)
 			dev->use_dma = true;
 	}
 
-	at91_calc_twi_clock(dev, TWI_CLK_HZ);
+	rc = of_property_read_u32(dev->dev->of_node, "clock-frequency",
+			&bus_clk_rate);
+	if (rc)
+		bus_clk_rate = DEFAULT_TWI_CLK_HZ;
+
+	at91_calc_twi_clock(dev, bus_clk_rate);
 	at91_init_twi_bus(dev);
 
 	snprintf(dev->adapter.name, sizeof(dev->adapter.name), "AT91");
-- 
1.7.10.4