mfd: syscon: Add optional clock support

Some system control registers need to be clocked, so the registers can
be accessed. Add an optional clock and attach it to regmap.
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/syscon.c

@@ -12,6 +12,7 @@
  * (at your option) any later version.
  */
 
+#include <linux/clk.h>
 #include <linux/err.h>
 #include <linux/hwspinlock.h>
 #include <linux/io.h>
@@ -45,6 +46,7 @@ static const struct regmap_config syscon_regmap_config = {
 
 static struct syscon *of_syscon_register(struct device_node *np)
 {
+	struct clk *clk;
 	struct syscon *syscon;
 	struct regmap *regmap;
 	void __iomem *base;
@@ -119,6 +121,18 @@ static struct syscon *of_syscon_register(struct device_node *np)
 		goto err_regmap;
 	}
 
+	clk = of_clk_get(np, 0);
+	if (IS_ERR(clk)) {
+		ret = PTR_ERR(clk);
+		/* clock is optional */
+		if (ret != -ENOENT)
+			goto err_clk;
+	} else {
+		ret = regmap_mmio_attach_clk(regmap, clk);
+		if (ret)
+			goto err_attach;
+	}
+
 	syscon->regmap = regmap;
 	syscon->np = np;
 
@@ -128,6 +142,11 @@ static struct syscon *of_syscon_register(struct device_node *np)
 
 	return syscon;
 
+err_attach:
+	if (!IS_ERR(clk))
+		clk_put(clk);
+err_clk:
+	regmap_exit(regmap);
 err_regmap:
 	iounmap(base);
 err_map: