Re: [PATCH v5 12/14] media: ov772x: avoid accessing registers under power saving mode

[Sakari Ailus <sakari.ailus@linux.intel.com>]

Hi Jacopo,

On Mon, May 14, 2018 at 11:06:46AM +0200, jacopo mondi wrote:
> Hi Akinobu,
> 
>    a small nit below
> 
> On Sun, May 06, 2018 at 11:19:27PM +0900, Akinobu Mita wrote:
> > 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>
> > ---
> > * v5
> > - No changes
> >
> >  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 9292a18..262a7e5 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;
> > @@ -885,6 +906,10 @@ 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);
> > @@ -895,8 +920,20 @@ 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. */
> > @@ -1163,7 +1200,7 @@ 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;
> > @@ -1184,14 +1221,24 @@ 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)
> > @@ -1201,7 +1248,7 @@ 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;
> >
> > @@ -1241,7 +1288,7 @@ 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;
> >  }
> > @@ -1340,6 +1387,8 @@ 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;
> 
> Isn't this unrelated?

AFAICT not, since the access to power count is serialised using the
driver's mutex. The power count is used in the s_ctrl callback as well.

> 
> Apart from that,
> 
> Reviewed-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> 
> Thanks
>   j
> 
> 
> >  	priv->vflip_ctrl = v4l2_ctrl_new_std(&priv->hdl, &ov772x_ctrl_ops,
> >  					     V4L2_CID_VFLIP, 0, 1, 1, 0);
> >  	priv->hflip_ctrl = v4l2_ctrl_new_std(&priv->hdl, &ov772x_ctrl_ops,
> > --
> > 2.7.4
> >



-- 
Sakari Ailus
sakari.ailus@linux.intel.com