cpufreq: imx6q: read OCOTP through nvmem for imx6ul/imx6ull

On i.MX6UL/i.MX6ULL, accessing OCOTP directly is wrong because
the ocotp clock needs to be enabled first. Add support for reading
OCOTP through the nvmem API, and keep the old method there to
support old dtb.
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/cpufreq/imx6q-cpufreq.c

@@ -12,6 +12,7 @@
 #include <linux/cpu_cooling.h>
 #include <linux/err.h>
 #include <linux/module.h>
+#include <linux/nvmem-consumer.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
 #include <linux/pm_opp.h>
@@ -290,20 +291,32 @@ static void imx6q_opp_check_speed_grading(struct device *dev)
 #define OCOTP_CFG3_6ULL_SPEED_792MHZ	0x2
 #define OCOTP_CFG3_6ULL_SPEED_900MHZ	0x3
 
-static void imx6ul_opp_check_speed_grading(struct device *dev)
+static int imx6ul_opp_check_speed_grading(struct device *dev)
 {
+	u32 val;
+	int ret = 0;
+
+	if (of_find_property(dev->of_node, "nvmem-cells", NULL)) {
+		ret = nvmem_cell_read_u32(dev, "speed_grade", &val);
+		if (ret)
+			return ret;
+	} else {
 		struct device_node *np;
 		void __iomem *base;
-	u32 val;
 
 		np = of_find_compatible_node(NULL, NULL, "fsl,imx6ul-ocotp");
 		if (!np)
-		return;
+			return -ENOENT;
 
 		base = of_iomap(np, 0);
+		of_node_put(np);
 		if (!base) {
 			dev_err(dev, "failed to map ocotp\n");
-		goto put_node;
+			return -EFAULT;
+		}
+
+		val = readl_relaxed(base + OCOTP_CFG3);
+		iounmap(base);
 	}
 
 	/*
@@ -314,7 +327,6 @@ static void imx6ul_opp_check_speed_grading(struct device *dev)
 	 * 2b'11: 900000000Hz on i.MX6ULL only;
 	 * We need to set the max speed of ARM according to fuse map.
 	 */
-	val = readl_relaxed(base + OCOTP_CFG3);
 	val >>= OCOTP_CFG3_SPEED_SHIFT;
 	val &= 0x3;
 
@@ -334,9 +346,7 @@ static void imx6ul_opp_check_speed_grading(struct device *dev)
 				dev_warn(dev, "failed to disable 900MHz OPP\n");
 	}
 
-	iounmap(base);
-put_node:
-	of_node_put(np);
+	return ret;
 }
 
 static int imx6q_cpufreq_probe(struct platform_device *pdev)
@@ -394,10 +404,18 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
 	}
 
 	if (of_machine_is_compatible("fsl,imx6ul") ||
-	    of_machine_is_compatible("fsl,imx6ull"))
-		imx6ul_opp_check_speed_grading(cpu_dev);
-	else
+	    of_machine_is_compatible("fsl,imx6ull")) {
+		ret = imx6ul_opp_check_speed_grading(cpu_dev);
+		if (ret == -EPROBE_DEFER)
+			return ret;
+		if (ret) {
+			dev_err(cpu_dev, "failed to read ocotp: %d\n",
+				ret);
+			return ret;
+		}
+	} else {
 		imx6q_opp_check_speed_grading(cpu_dev);
+	}
 
 	/* Because we have added the OPPs here, we must free them */
 	free_opp = true;