mfd: Use bulk read to fill WM8350 register cache

Some I2C controllers have high overheads for setting up I2C operations
which makes the register cache setup on startup excessively slow since
it does a lot of small transactions. Reduce this overhead by doing a
bulk read of the entire register bank and filtering out what we don't
need later.
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NSamuel Ortiz <sameo@openedhand.com>

drivers/mfd/wm8350-core.c

@@ -1238,7 +1238,7 @@ static int wm8350_create_cache(struct wm8350 *wm8350, int type, int mode)
 	}
 
 	wm8350->reg_cache =
-	    kzalloc(sizeof(u16) * (WM8350_MAX_REGISTER + 1), GFP_KERNEL);
+		kmalloc(sizeof(u16) * (WM8350_MAX_REGISTER + 1), GFP_KERNEL);
 	if (wm8350->reg_cache == NULL)
 		return -ENOMEM;
 
@@ -1246,17 +1246,20 @@ static int wm8350_create_cache(struct wm8350 *wm8350, int type, int mode)
 	 * a PMIC so the device many not be in a virgin state and we
 	 * can't rely on the silicon values.
 	 */
+	ret = wm8350->read_dev(wm8350, 0,
+			       sizeof(u16) * (WM8350_MAX_REGISTER + 1),
+			       wm8350->reg_cache);
+	if (ret < 0) {
+		dev_err(wm8350->dev,
+			"failed to read initial cache values\n");
+		goto out;
+	}
+
+	/* Mask out uncacheable/unreadable bits and the audio. */
 	for (i = 0; i < WM8350_MAX_REGISTER; i++) {
-		/* audio register range */
 		if (wm8350_reg_io_map[i].readable &&
 		    (i < WM8350_CLOCK_CONTROL_1 || i > WM8350_AIF_TEST)) {
-			ret = wm8350->read_dev(wm8350, i, 2, (char *)&value);
-			if (ret < 0) {
-				dev_err(wm8350->dev,
-				       "failed to read initial cache value\n");
-				goto out;
-			}
-			value = be16_to_cpu(value);
+			value = be16_to_cpu(wm8350->reg_cache[i]);
 			value &= wm8350_reg_io_map[i].readable;
 			value &= ~wm8350_reg_io_map[i].vol;
 			wm8350->reg_cache[i] = value;