nvmem: imx-ocotp: handling clock

Before access ocotp nvmem area, the clock should be enabled.
Or, `hexdump nvmem` will hang the system. So, use such flow:
"
  1. clock_enable_prepare
  2. read nvmem ocotp area
  3. clock_disable_unprepare
"
Signed-off-by: Peng Fan <van.freenix@gmail.com>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/nvmem/imx-ocotp.c

@@ -15,6 +15,7 @@
  * http://www.gnu.org/copyleft/gpl.html
  */
 
+#include <linux/clk.h>
 #include <linux/device.h>
 #include <linux/io.h>
 #include <linux/module.h>
@@ -26,6 +27,7 @@
 
 struct ocotp_priv {
 	struct device *dev;
+	struct clk *clk;
 	void __iomem *base;
 	unsigned int nregs;
 };
@@ -36,7 +38,7 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 	struct ocotp_priv *priv = context;
 	unsigned int count;
 	u32 *buf = val;
-	int i;
+	int i, ret;
 	u32 index;
 
 	index = offset >> 2;
@@ -45,9 +47,16 @@ static int imx_ocotp_read(void *context, unsigned int offset,
 	if (count > (priv->nregs - index))
 		count = priv->nregs - index;
 
+	ret = clk_prepare_enable(priv->clk);
+	if (ret < 0) {
+		dev_err(priv->dev, "failed to prepare/enable ocotp clk\n");
+		return ret;
+	}
 	for (i = index; i < (index + count); i++)
 		*buf++ = readl(priv->base + 0x400 + i * 0x10);
 
+	clk_disable_unprepare(priv->clk);
+
 	return 0;
 }
 
@@ -85,6 +94,10 @@ static int imx_ocotp_probe(struct platform_device *pdev)
 	if (IS_ERR(priv->base))
 		return PTR_ERR(priv->base);
 
+	priv->clk = devm_clk_get(&pdev->dev, NULL);
+	if (IS_ERR(priv->clk))
+		return PTR_ERR(priv->clk);
+
 	of_id = of_match_device(imx_ocotp_dt_ids, dev);
 	priv->nregs = (unsigned int)of_id->data;
 	imx_ocotp_nvmem_config.size = 4 * priv->nregs;