regulator: fixed: obey startup delay

When enabling a fixed regulator, it may take some time to rise to the
correct voltage.  If we do not delay here then subsequent operations
will fail.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

doc/device-tree-bindings/regulator/fixed.txt

@@ -10,6 +10,7 @@ Required properties:
 
 Optional properties:
 - gpio: GPIO to use for enable control
+- startup-delay-us: startup time in microseconds
 - regulator constraints (binding info: regulator.txt)
 
 Other kernel-style properties, are currently not used.

drivers/power/regulator/fixed.c

@@ -19,6 +19,7 @@ DECLARE_GLOBAL_DATA_PTR;
 
 struct fixed_regulator_platdata {
 	struct gpio_desc gpio; /* GPIO for regulator enable control */
+	unsigned int startup_delay_us;
 };
 
 static int fixed_regulator_ofdata_to_platdata(struct udevice *dev)
@@ -42,6 +43,11 @@ static int fixed_regulator_ofdata_to_platdata(struct udevice *dev)
 	if (ret)
 		debug("Fixed regulator gpio - not found! Error: %d", ret);
 
+	/* Get optional ramp up delay */
+	dev_pdata->startup_delay_us = fdtdec_get_uint(gd->fdt_blob,
+						      dev->of_offset,
+						      "startup-delay-us", 0);
+
 	return 0;
 }
 
@@ -101,6 +107,10 @@ static int fixed_regulator_set_enable(struct udevice *dev, bool enable)
 		      enable);
 		return ret;
 	}
+
+	if (enable && dev_pdata->startup_delay_us)
+		udelay(dev_pdata->startup_delay_us);
+
 	return 0;
 }