[PATCH v3 09/11] media: ov772x: avoid accessing registers under power saving mode

[Akinobu Mita <akinobu.mita@gmail.com>]

The set_fmt() in subdev pad ops, the s_ctrl() for subdev control handler,
and the s_frame_interval() in subdev video ops could be called when the
device is under power saving mode.  These callbacks for ov772x driver
cause updating H/W registers that will fail under power saving mode.

This avoids it by not apply any changes to H/W if the device is not powered
up.  Instead the changes will be restored right after power-up.

Cc: Jacopo Mondi <jacopo+renesas@jmondi.org>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Sakari Ailus <sakari.ailus@linux.intel.com>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
---
* v3
- Add newlines before labels
- Remove __v4l2_ctrl_handler_setup in s_power() as it causes duplicated
  register settings

 drivers/media/i2c/ov772x.c | 79 +++++++++++++++++++++++++++++++++++++---------
 1 file changed, 64 insertions(+), 15 deletions(-)

diff --git a/drivers/media/i2c/ov772x.c b/drivers/media/i2c/ov772x.c
index 452406c..96dd37a 100644
--- a/drivers/media/i2c/ov772x.c
+++ b/drivers/media/i2c/ov772x.c
@@ -741,19 +741,30 @@ static int ov772x_s_frame_interval(struct v4l2_subdev *sd,
 	struct ov772x_priv *priv = to_ov772x(sd);
 	struct v4l2_fract *tpf = &ival->interval;
 	unsigned int fps;
-	int ret;
+	int ret = 0;
 
 	fps = ov772x_select_fps(priv, tpf);
 
-	ret = ov772x_set_frame_rate(priv, fps, priv->cfmt, priv->win);
-	if (ret)
-		return ret;
+	mutex_lock(&priv->lock);
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any changes to H/W at this time. Instead
+	 * the frame rate will be restored right after power-up.
+	 */
+	if (priv->power_count > 0) {
+		ret = ov772x_set_frame_rate(priv, fps, priv->cfmt, priv->win);
+		if (ret)
+			goto error;
+	}
 
 	tpf->numerator = 1;
 	tpf->denominator = fps;
 	priv->fps = fps;
 
-	return 0;
+error:
+	mutex_unlock(&priv->lock);
+
+	return ret;
 }
 
 static int ov772x_s_ctrl(struct v4l2_ctrl *ctrl)
@@ -765,6 +776,16 @@ static int ov772x_s_ctrl(struct v4l2_ctrl *ctrl)
 	int ret = 0;
 	u8 val;
 
+	/* v4l2_ctrl_lock() locks our own mutex */
+
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any controls to H/W at this time. Instead
+	 * the controls will be restored right after power-up.
+	 */
+	if (priv->power_count == 0)
+		return 0;
+
 	switch (ctrl->id) {
 	case V4L2_CID_VFLIP:
 		val = ctrl->val ? VFLIP_IMG : 0x00;
@@ -888,6 +909,10 @@ static int ov772x_power_off(struct ov772x_priv *priv)
 	return 0;
 }
 
+static int ov772x_set_params(struct ov772x_priv *priv,
+			     const struct ov772x_color_format *cfmt,
+			     const struct ov772x_win_size *win);
+
 static int ov772x_s_power(struct v4l2_subdev *sd, int on)
 {
 	struct ov772x_priv *priv = to_ov772x(sd);
@@ -898,8 +923,20 @@ static int ov772x_s_power(struct v4l2_subdev *sd, int on)
 	/* If the power count is modified from 0 to != 0 or from != 0 to 0,
 	 * update the power state.
 	 */
-	if (priv->power_count == !on)
-		ret = on ? ov772x_power_on(priv) : ov772x_power_off(priv);
+	if (priv->power_count == !on) {
+		if (on) {
+			ret = ov772x_power_on(priv);
+			/*
+			 * Restore the format, the frame rate, and
+			 * the controls
+			 */
+			if (!ret)
+				ret = ov772x_set_params(priv, priv->cfmt,
+							priv->win);
+		} else {
+			ret = ov772x_power_off(priv);
+		}
+	}
 
 	if (!ret) {
 		/* Update the power count. */
@@ -1164,7 +1201,7 @@ static int ov772x_set_fmt(struct v4l2_subdev *sd,
 	struct v4l2_mbus_framefmt *mf = &format->format;
 	const struct ov772x_color_format *cfmt;
 	const struct ov772x_win_size *win;
-	int ret;
+	int ret = 0;
 
 	if (format->pad)
 		return -EINVAL;
@@ -1185,14 +1222,24 @@ static int ov772x_set_fmt(struct v4l2_subdev *sd,
 		return 0;
 	}
 
-	ret = ov772x_set_params(priv, cfmt, win);
-	if (ret < 0)
-		return ret;
-
+	mutex_lock(&priv->lock);
+	/*
+	 * If the device is not powered up by the host driver do
+	 * not apply any changes to H/W at this time. Instead
+	 * the format will be restored right after power-up.
+	 */
+	if (priv->power_count > 0) {
+		ret = ov772x_set_params(priv, cfmt, win);
+		if (ret < 0)
+			goto error;
+	}
 	priv->win = win;
 	priv->cfmt = cfmt;
 
-	return 0;
+error:
+	mutex_unlock(&priv->lock);
+
+	return ret;
 }
 
 static int ov772x_video_probe(struct ov772x_priv *priv)
@@ -1202,7 +1249,7 @@ static int ov772x_video_probe(struct ov772x_priv *priv)
 	const char         *devname;
 	int		    ret;
 
-	ret = ov772x_s_power(&priv->subdev, 1);
+	ret = ov772x_power_on(priv);
 	if (ret < 0)
 		return ret;
 
@@ -1242,7 +1289,7 @@ static int ov772x_video_probe(struct ov772x_priv *priv)
 	ret = v4l2_ctrl_handler_setup(&priv->hdl);
 
 done:
-	ov772x_s_power(&priv->subdev, 0);
+	ov772x_power_off(priv);
 
 	return ret;
 }
@@ -1341,6 +1388,8 @@ static int ov772x_probe(struct i2c_client *client,
 
 	v4l2_i2c_subdev_init(&priv->subdev, client, &ov772x_subdev_ops);
 	v4l2_ctrl_handler_init(&priv->hdl, 3);
+	/* Use our mutex for the controls */
+	priv->hdl.lock = &priv->lock;
 	v4l2_ctrl_new_std(&priv->hdl, &ov772x_ctrl_ops,
 			  V4L2_CID_VFLIP, 0, 1, 1, 0);
 	v4l2_ctrl_new_std(&priv->hdl, &ov772x_ctrl_ops,
-- 
2.7.4