iio: adc: aspeed: Deassert reset in probe

The ASPEED SoC must deassert a reset in order to use the ADC peripheral.

The device tree bindings are updated to document the resets phandle, and
the example is updated to match what is expected for both the reset and
clock phandle. Note that the bindings should have always had the reset
controller, as the hardware is unusable without it.
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/aspeed_adc.txt

@@ -8,6 +8,7 @@ Required properties:
 - reg: memory window mapping address and length
 - clocks: Input clock used to derive the sample clock. Expected to be the
           SoC's APB clock.
+- resets: Reset controller phandle
 - #io-channel-cells: Must be set to <1> to indicate channels are selected
                      by index.
 
@@ -15,6 +16,7 @@ Example:
 	adc@1e6e9000 {
 		compatible = "aspeed,ast2400-adc";
 		reg = <0x1e6e9000 0xb0>;
-		clocks = <&clk_apb>;
+		clocks = <&syscon ASPEED_CLK_APB>;
+		resets = <&syscon ASPEED_RESET_ADC>;
 		#io-channel-cells = <1>;
 	};

drivers/iio/adc/aspeed_adc.c

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 #include <linux/spinlock.h>
 #include <linux/types.h>
 
@@ -58,6 +59,7 @@ struct aspeed_adc_data {
 	spinlock_t		clk_lock;
 	struct clk_hw		*clk_prescaler;
 	struct clk_hw		*clk_scaler;
+	struct reset_control	*rst;
 };
 
 #define ASPEED_CHAN(_idx, _data_reg_addr) {			\
@@ -217,6 +219,15 @@ static int aspeed_adc_probe(struct platform_device *pdev)
 		goto scaler_error;
 	}
 
+	data->rst = devm_reset_control_get_exclusive(&pdev->dev, NULL);
+	if (IS_ERR(data->rst)) {
+		dev_err(&pdev->dev,
+			"invalid or missing reset controller device tree entry");
+		ret = PTR_ERR(data->rst);
+		goto reset_error;
+	}
+	reset_control_deassert(data->rst);
+
 	model_data = of_device_get_match_data(&pdev->dev);
 
 	if (model_data->wait_init_sequence) {
@@ -263,9 +274,10 @@ static int aspeed_adc_probe(struct platform_device *pdev)
 	writel(ASPEED_OPERATION_MODE_POWER_DOWN,
 		data->base + ASPEED_REG_ENGINE_CONTROL);
 	clk_disable_unprepare(data->clk_scaler->clk);
+reset_error:
+	reset_control_assert(data->rst);
 clk_enable_error:
 	clk_hw_unregister_divider(data->clk_scaler);
-
 scaler_error:
 	clk_hw_unregister_divider(data->clk_prescaler);
 	return ret;
@@ -280,6 +292,7 @@ static int aspeed_adc_remove(struct platform_device *pdev)
 	writel(ASPEED_OPERATION_MODE_POWER_DOWN,
 		data->base + ASPEED_REG_ENGINE_CONTROL);
 	clk_disable_unprepare(data->clk_scaler->clk);
+	reset_control_assert(data->rst);
 	clk_hw_unregister_divider(data->clk_scaler);
 	clk_hw_unregister_divider(data->clk_prescaler);