Re: [PATCH v4 05/29] media: imx219: Fix vertical blanking and exposure for analogue binning

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi Sakari

On Fri, Apr 10, 2026 at 11:46:49AM +0300, Sakari Ailus wrote:
> Hi Jacopo,
>
> On Fri, Apr 10, 2026 at 10:42:22AM +0200, Jacopo Mondi wrote:
> > Hi Sakari
> >
> > On Wed, Apr 08, 2026 at 06:39:14PM +0300, Sakari Ailus wrote:
> > > When vertical analogue binning is in use, the minimum frame length in
> > > lines decreases to around half of the normal. In relation to the sensor's
> > > output size this means vertical blanking can be negative but that's not an
> > > issue as control values are signed. Remove the workaround for this
> > > non-issue that doubled the pixel rate, frame length in lines and exposure
> > > time.
> >
> > I don't think this was a workaround. Doubling the pixel rate and
>
> You could also call it a bug. :-) If you look what the driver does with
> PLL, you can see the PLL configuration is always the same independently of
> any binning configuration.

Are you suggesting doubling the PIXEL_RATE is not accurate as the PLL
config doesn't change ? I might be very wrong, but in my understanding
this is partially why the "special" binning mode is special. We don't
have documentation for it and I'm maybe speculating here.

Is doubling the VBLANK limit to a number larger of the register
maximum value more accurate ?

>
> > halving the values written to registers for EXPOSURE and VBLANK
> > allowed userspace to maintain a consistent view while the driver
> > accounts for the special binning mode where, at least in my latest
> > understanding, the sensor averages two lines before passing them to
> > the ADC.
> >
> > I am missing in which case, with the current driver implementation,
> > the vertical blanking can be negative.
> >
> > >
> > > The resulting change also fixes the minimum, the maximum and the step
> > > values for the control.
> > >
> > > Fixes: f513997119f4 ("media: i2c: imx219: Scale the pixel rate for analog binning")
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> >
> > Jai, and others including Dave and me, have spent quite some time
> > testing and implementing proper support for the special analogue
> > binning mode for this sensor. Of course we might have missed something
> > obvious, but I'm still missing what you're trying to fix here.
> >

still not sure what you're trying to fix here

> > > ---
> > >  drivers/media/i2c/imx219.c | 29 +++++++++--------------------
> > >  1 file changed, 9 insertions(+), 20 deletions(-)
> > >
> > > diff --git a/drivers/media/i2c/imx219.c b/drivers/media/i2c/imx219.c
> > > index 6819a2fa3262..a72630ad1561 100644
> > > --- a/drivers/media/i2c/imx219.c
> > > +++ b/drivers/media/i2c/imx219.c
> > > @@ -420,15 +420,6 @@ static void imx219_get_binning(struct v4l2_subdev_state *state, u8 *bin_h,
> > >
> > >  }
> > >
> > > -static inline u32 imx219_get_rate_factor(struct v4l2_subdev_state *state)
> > > -{
> > > -	u8 bin_h, bin_v;
> > > -
> > > -	imx219_get_binning(state, &bin_h, &bin_v);
> > > -
> > > -	return (bin_h & bin_v) == IMX219_BINNING_X2_ANALOG ? 2 : 1;
> > > -}
> > > -
> > >  /* -----------------------------------------------------------------------------
> > >   * Controls
> > >   */
> > > @@ -440,12 +431,10 @@ static int imx219_set_ctrl(struct v4l2_ctrl *ctrl)
> > >  	struct i2c_client *client = v4l2_get_subdevdata(&imx219->sd);
> > >  	const struct v4l2_mbus_framefmt *format;
> > >  	struct v4l2_subdev_state *state;
> > > -	u32 rate_factor;
> > >  	int ret = 0;
> > >
> > >  	state = v4l2_subdev_get_locked_active_state(&imx219->sd);
> > >  	format = v4l2_subdev_state_get_format(state, 0);
> > > -	rate_factor = imx219_get_rate_factor(state);
> > >
> > >  	if (ctrl->id == V4L2_CID_VBLANK) {
> > >  		int exposure_max, exposure_def;
> > > @@ -478,7 +467,7 @@ static int imx219_set_ctrl(struct v4l2_ctrl *ctrl)
> > >  		break;
> > >  	case V4L2_CID_EXPOSURE:
> > >  		cci_write(imx219->regmap, IMX219_REG_EXPOSURE,
> > > -			  ctrl->val / rate_factor, &ret);
> > > +			  ctrl->val, &ret);
> > >  		break;
> > >  	case V4L2_CID_DIGITAL_GAIN:
> > >  		cci_write(imx219->regmap, IMX219_REG_DIGITAL_GAIN,
> > > @@ -495,7 +484,7 @@ static int imx219_set_ctrl(struct v4l2_ctrl *ctrl)
> > >  		break;
> > >  	case V4L2_CID_VBLANK:
> > >  		cci_write(imx219->regmap, IMX219_REG_FRM_LENGTH_A,
> > > -			  (format->height + ctrl->val) / rate_factor, &ret);
> > > +			  format->height + ctrl->val, &ret);
> > >  		break;
> > >  	case V4L2_CID_HBLANK:
> > >  		cci_write(imx219->regmap, IMX219_REG_LINE_LENGTH_A,
> > > @@ -878,7 +867,6 @@ static int imx219_set_pad_format(struct v4l2_subdev *sd,
> > >  	crop->top = (IMX219_NATIVE_HEIGHT - crop->height) / 2;
> > >
> > >  	if (fmt->which == V4L2_SUBDEV_FORMAT_ACTIVE) {
> > > -		unsigned int rate_factor = imx219_get_rate_factor(state);
> > >  		int exposure_max;
> > >  		int exposure_def;
> > >  		int llp_min;
> > > @@ -886,15 +874,16 @@ static int imx219_set_pad_format(struct v4l2_subdev *sd,
> > >
> > >  		/* Update limits and set FPS to default */
> > >  		ret = __v4l2_ctrl_modify_range(imx219->vblank,
> > > -					       IMX219_VBLANK_MIN * rate_factor,
> > > -					       (IMX219_FLL_MAX - mode->height) *
> > > -					       rate_factor, rate_factor,
> > > -					       mode->fll_def - mode->height);
> > > +					       (int)(mode->height / binning),
> > > +					       IMX219_FLL_MAX - mode->height, 1,
> > > +					       (int)(mode->fll_def / binning) -
> > > +					       (int)mode->height);
> > >  		if (ret)
> > >  			return ret;
> > >
> > >  		ret = __v4l2_ctrl_s_ctrl(imx219->vblank,
> > > -					 mode->fll_def - mode->height);
> > > +					 (int)(mode->fll_def / binning) -
> > > +					 (int)mode->height);
> > >  		if (ret)
> > >  			return ret;
> > >
> > > @@ -931,7 +920,7 @@ static int imx219_set_pad_format(struct v4l2_subdev *sd,
> > >  			return ret;
> > >
> > >  		/* Scale the pixel rate based on the mode specific factor */
> > > -		pixel_rate = imx219_get_pixel_rate(imx219) * rate_factor;
> > > +		pixel_rate = imx219_get_pixel_rate(imx219);
> > >  		ret = __v4l2_ctrl_modify_range(imx219->pixel_rate, pixel_rate,
> > >  					       pixel_rate, 1, pixel_rate);
> > >  		if (ret)
>
> --
> Regards,
>
> Sakari Ailus
>