Input: snvs_pwrkey - add clk handling

On i.MX7S and i.MX8M* (but not i.MX6*) the pwrkey device has an
associated clock. Accessing the registers requires that this clock is
enabled. Binding the driver on at least i.MX7S and i.MX8MP while not
having the clock enabled results in a complete hang of the machine.
(This usually only happens if snvs_pwrkey is built as a module and the
rtc-snvs driver isn't already bound because at bootup the required clk
is on and only gets disabled when the clk framework disables unused clks
late during boot.)

This completes the fix in commit 135be16d ("ARM: dts: imx7s: add
snvs clock to pwrkey").
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20211013062848.2667192-1-u.kleine-koenig@pengutronix.deSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/keyboard/snvs_pwrkey.c

@@ -3,6 +3,7 @@
 // Driver for the IMX SNVS ON/OFF Power Key
 // Copyright (C) 2015 Freescale Semiconductor, Inc. All Rights Reserved.
 
+#include <linux/clk.h>
 #include <linux/device.h>
 #include <linux/err.h>
 #include <linux/init.h>
@@ -99,6 +100,11 @@ static irqreturn_t imx_snvs_pwrkey_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
+static void imx_snvs_pwrkey_disable_clk(void *data)
+{
+	clk_disable_unprepare(data);
+}
+
 static void imx_snvs_pwrkey_act(void *pdata)
 {
 	struct pwrkey_drv_data *pd = pdata;
@@ -111,6 +117,7 @@ static int imx_snvs_pwrkey_probe(struct platform_device *pdev)
 	struct pwrkey_drv_data *pdata;
 	struct input_dev *input;
 	struct device_node *np;
+	struct clk *clk;
 	int error;
 	u32 vid;
 
@@ -134,6 +141,28 @@ static int imx_snvs_pwrkey_probe(struct platform_device *pdev)
 		dev_warn(&pdev->dev, "KEY_POWER without setting in dts\n");
 	}
 
+	clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(&pdev->dev, "Failed to get snvs clock (%pe)\n", clk);
+		return PTR_ERR(clk);
+	}
+
+	error = clk_prepare_enable(clk);
+	if (error) {
+		dev_err(&pdev->dev, "Failed to enable snvs clock (%pe)\n",
+			ERR_PTR(error));
+		return error;
+	}
+
+	error = devm_add_action_or_reset(&pdev->dev,
+					 imx_snvs_pwrkey_disable_clk, clk);
+	if (error) {
+		dev_err(&pdev->dev,
+			"Failed to register clock cleanup handler (%pe)\n",
+			ERR_PTR(error));
+		return error;
+	}
+
 	pdata->wakeup = of_property_read_bool(np, "wakeup-source");
 
 	pdata->irq = platform_get_irq(pdev, 0);