i2c: aspeed: Deassert reset in probe

In order to use i2c from a cold boot, the i2c peripheral must be taken
out of reset. We request a shared reset controller each time a bus
driver is loaded, as the reset is shared between the 14 i2c buses.

On remove the reset is asserted, which only touches the hardware once
the last i2c bus is removed.

The reset is required as the I2C buses will not work without releasing
the reset. Previously the driver only worked with out of tree hacks
that released this reset before the driver was loaded. Update the
device tree bindings to reflect this.
Signed-off-by: Joel Stanley <joel@jms.id.au>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

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

@@ -7,7 +7,9 @@ Required Properties:
 - compatible		: should be "aspeed,ast2400-i2c-bus"
 			  or "aspeed,ast2500-i2c-bus"
 - clocks		: root clock of bus, should reference the APB
-			  clock
+			  clock in the second cell
+- resets		: phandle to reset controller with the reset number in
+			  the second cell
 - interrupts		: interrupt number
 - interrupt-parent	: interrupt controller for bus, should reference a
 			  aspeed,ast2400-i2c-ic or aspeed,ast2500-i2c-ic
@@ -40,7 +42,8 @@ i2c {
 		#interrupt-cells = <1>;
 		reg = <0x40 0x40>;
 		compatible = "aspeed,ast2400-i2c-bus";
-		clocks = <&clk_apb>;
+		clocks = <&syscon ASPEED_CLK_APB>;
+		resets = <&syscon ASPEED_RESET_I2C>;
 		bus-frequency = <100000>;
 		interrupts = <0>;
 		interrupt-parent = <&i2c_ic>;

drivers/i2c/busses/i2c-aspeed.c

@@ -27,6 +27,7 @@
 #include <linux/of_irq.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 #include <linux/slab.h>
 
 /* I2C Register */
@@ -132,6 +133,7 @@ struct aspeed_i2c_bus {
 	struct i2c_adapter		adap;
 	struct device			*dev;
 	void __iomem			*base;
+	struct reset_control		*rst;
 	/* Synchronizes I/O mem access to base. */
 	spinlock_t			lock;
 	struct completion		cmd_complete;
@@ -847,6 +849,14 @@ static int aspeed_i2c_probe_bus(struct platform_device *pdev)
 	/* We just need the clock rate, we don't actually use the clk object. */
 	devm_clk_put(&pdev->dev, parent_clk);
 
+	bus->rst = devm_reset_control_get_shared(&pdev->dev, NULL);
+	if (IS_ERR(bus->rst)) {
+		dev_err(&pdev->dev,
+			"missing or invalid reset controller device tree entry");
+		return PTR_ERR(bus->rst);
+	}
+	reset_control_deassert(bus->rst);
+
 	ret = of_property_read_u32(pdev->dev.of_node,
 				   "bus-frequency", &bus->bus_frequency);
 	if (ret < 0) {
@@ -917,6 +927,8 @@ static int aspeed_i2c_remove_bus(struct platform_device *pdev)
 
 	spin_unlock_irqrestore(&bus->lock, flags);
 
+	reset_control_assert(bus->rst);
+
 	i2c_del_adapter(&bus->adap);
 
 	return 0;