Re: [PATCH v2] media: i2c: imx219: Implement get_selection

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Jacopo,

On Tue, Apr 28, 2020 at 03:40:36PM +0200, Jacopo Mondi wrote:
> On Mon, Apr 27, 2020 at 12:05:48AM +0300, Laurent Pinchart wrote:
> > Hi Jacopo,
> >
> > Thank you for the patch.
> >
> 
> [snip]
> 
> > > +
> > > +static int imx219_get_selection(struct v4l2_subdev *sd,
> > > +				struct v4l2_subdev_pad_config *cfg,
> > > +				struct v4l2_subdev_selection *sel)
> > > +{
> > > +	struct imx219 *imx219 = to_imx219(sd);
> > > +	const struct v4l2_rect *__crop;
> > > +
> > > +	if (sel->pad != 0)
> > > +		return -EINVAL;
> > > +
> > > +	mutex_lock(&imx219->mutex);
> > > +
> > > +	switch (sel->target) {
> > > +	case V4L2_SEL_TGT_NATIVE_SIZE:
> > > +		sel->r.top = 0;
> > > +		sel->r.left = 0;
> > > +		sel->r.width = IMX219_NATIVE_WIDTH;
> > > +		sel->r.height = IMX219_NATIVE_HEIGHT;
> > > +		mutex_unlock(&imx219->mutex);
> > > +
> > > +		return 0;
> > > +
> > > +	case V4L2_SEL_TGT_CROP_DEFAULT:
> > > +		sel->r.top = IMX219_PIXEL_ARRAY_TOP;
> > > +		sel->r.left = IMX219_PIXEL_ARRAY_LEFT;
> > > +		sel->r.width = IMX219_PIXEL_ARRAY_WIDTH;
> > > +		sel->r.height = IMX219_PIXEL_ARRAY_HEIGHT;
> > > +		mutex_unlock(&imx219->mutex);
> > > +
> > > +		return 0;
> > > +
> > > +	case V4L2_SEL_TGT_CROP:
> > > +		__crop = __imx219_get_pad_crop(imx219, cfg, sel->pad,
> > > +					       sel->which);
> > > +		sel->r = *__crop;
> > > +		mutex_unlock(&imx219->mutex);
> >
> > I should have thought about it before, but only this case requires
> > locking. Maybe
> 
> I should have thought it better, yes
> 
> >
> > 		__crop = __imx219_get_pad_crop(imx219, cfg, sel->pad,
> > 					       sel->which);
> > 		mutex_lock(&imx219->mutex);
> 
> Actually, retreiveing __crop should be protected too, as the crop
> rectangle is part of the imx219->mode, which is updated by the set_fmt
> operation.

__crop is a pointer, retrieving the pointer doesn't need protection.
Accessing its contents does. No big deal though, it's cheap, as long as
we don't lock for the bounds and default cases.

> I'll wrap the whole case content in a critical session.
> 
> > 		sel->r = *__crop;
> > 		mutex_unlock(&imx219->mutex);
> >
> > and removing the mutex_lock() at the beginning ?
> >
> > > +
> > > +		return 0;
> > > +	}
> > > +
> > > +	mutex_unlock(&imx219->mutex);
> > > +
> > > +	return -EINVAL;
> > > +}
> > > +
> > >  static int imx219_start_streaming(struct imx219 *imx219)
> > >  {
> > >  	struct i2c_client *client = v4l2_get_subdevdata(&imx219->sd);
> > > @@ -1152,6 +1248,7 @@ static const struct v4l2_subdev_pad_ops imx219_pad_ops = {
> > >  	.enum_mbus_code = imx219_enum_mbus_code,
> > >  	.get_fmt = imx219_get_pad_format,
> > >  	.set_fmt = imx219_set_pad_format,
> > > +	.get_selection = imx219_get_selection,
> > >  	.enum_frame_size = imx219_enum_frame_size,
> > >  };
> > >

-- 
Regards,

Laurent Pinchart