Staging/iio/adc/touchscreen/MXS: add proper clock handling

The delay units inside the LRADC depend on the presence of a 2 kHz clock.
This change enables the clock to be able to use the delay unit for the
touchscreen part of the driver.

Signed-off-by: Juergen Beisert <jbe@pengutronix.de>
Tested-by: Marek Vasut <marex@denx.de>
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

arch/arm/boot/dts/imx23.dtsi

@@ -430,6 +430,7 @@
 				reg = <0x80050000 0x2000>;
 				interrupts = <36 37 38 39 40 41 42 43 44>;
 				status = "disabled";
+				clocks = <&clks 26>;
 			};
 
 			spdif@80054000 {

arch/arm/boot/dts/imx28.dtsi

@@ -902,6 +902,7 @@
 				interrupts = <10 14 15 16 17 18 19
 						20 21 22 23 24 25>;
 				status = "disabled";
+				clocks = <&clks 41>;
 			};
 
 			spdif: spdif@80054000 {

drivers/staging/iio/adc/mxs-lradc.c

@@ -35,6 +35,7 @@
 #include <linux/completion.h>
 #include <linux/delay.h>
 #include <linux/input.h>
+#include <linux/clk.h>
 
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
@@ -134,6 +135,8 @@ struct mxs_lradc {
 	void __iomem		*base;
 	int			irq[13];
 
+	struct clk		*clk;
+
 	uint32_t		*buffer;
 	struct iio_trigger	*trig;
 
@@ -922,6 +925,17 @@ static int mxs_lradc_probe(struct platform_device *pdev)
 	if (IS_ERR(lradc->base))
 		return PTR_ERR(lradc->base);
 
+	lradc->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(lradc->clk)) {
+		dev_err(dev, "Failed to get the delay unit clock\n");
+		return PTR_ERR(lradc->clk);
+	}
+	ret = clk_prepare_enable(lradc->clk);
+	if (ret != 0) {
+		dev_err(dev, "Failed to enable the delay unit clock\n");
+		return ret;
+	}
+
 	INIT_WORK(&lradc->ts_work, mxs_lradc_ts_work);
 
 	/* Check if touchscreen is enabled in DT. */
@@ -1014,6 +1028,7 @@ static int mxs_lradc_remove(struct platform_device *pdev)
 	mxs_lradc_trigger_remove(iio);
 	iio_triggered_buffer_cleanup(iio);
 
+	clk_disable_unprepare(lradc->clk);
 	return 0;
 }