Re: [PATCH 3/3] media: i2c: max9286: Support manual framesync operation

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

Hi Jacopo,

On Fri, Dec 17, 2021 at 12:14:03PM +0100, Jacopo Mondi wrote:
> On Fri, Dec 17, 2021 at 12:09:46AM +0200, Laurent Pinchart wrote:
> > From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >
> > The MAX9286 can generate a framesync signal to synchronize the cameras,
> > using an internal timer. Support this mode of operation and configure it
> > through the .s_frameinterval() operation. If the frame interval is not
> > 0, framesync is switched to manual mode with the specified interval,
> > otherwise automatic mode is used.
> >
> > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > ---
> >  drivers/media/i2c/max9286.c | 66 +++++++++++++++++++++++++++++++++++--
> >  1 file changed, 63 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index fa2f6a823fe6..dce1146635d2 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -174,6 +174,7 @@ struct max9286_priv {
> >  	struct v4l2_ctrl *pixelrate;
> >
> >  	struct v4l2_mbus_framefmt fmt[MAX9286_N_SINKS];
> > +	struct v4l2_fract interval;
> >
> >  	/* Protects controls and fmt structures */
> >  	struct mutex mutex;
> > @@ -474,6 +475,37 @@ static int max9286_check_config_link(struct max9286_priv *priv,
> >  	return 0;
> >  }
> >
> > +static void max9286_set_fsync_period(struct max9286_priv *priv)
> > +{
> > +	u32 fsync;
> > +
> > +	if (!priv->interval.numerator || !priv->interval.denominator) {
> > +		/*
> > +		 * Special case, a null interval enables automatic FRAMESYNC
> > +		 * mode. FRAMESYNC is taken from the slowest link.
> > +		 */
> > +		max9286_write(priv, 0x01, MAX9286_FSYNCMODE_INT_HIZ |
> > +			      MAX9286_FSYNCMETH_AUTO);
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * Manual FRAMESYNC
> > +	 *
> > +	 * The FRAMESYNC generator is configured with a period expressed as a
> > +	 * number of PCLK periods, which runs at 75MHz.
> > +	 */
> > +	fsync = div_u64(75000000ULL * priv->interval.numerator,
> > +			priv->interval.denominator);
> 
> Don't we calculate the pixel rate dynamically based on the number of
> enabled sources ?

That's a good point, this hardcodes operation for 4 cameras. I'll see
how I can fix that.

> > +
> > +	max9286_write(priv, 0x01, MAX9286_FSYNCMODE_INT_OUT |
> > +		      MAX9286_FSYNCMETH_MANUAL);
> > +
> > +	max9286_write(priv, 0x06, (fsync >> 0) & 0xff);
> > +	max9286_write(priv, 0x07, (fsync >> 8) & 0xff);
> > +	max9286_write(priv, 0x08, (fsync >> 16) & 0xff);
> > +}
> > +
> >  /* -----------------------------------------------------------------------------
> >   * V4L2 Subdev
> >   */
> > @@ -656,6 +688,8 @@ static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> >  	int ret;
> >
> >  	if (enable) {
> > +		max9286_set_fsync_period(priv);
> > +
> >  		/*
> >  		 * The frame sync between cameras is transmitted across the
> >  		 * reverse channel as GPIO. We must open all channels while
> > @@ -715,6 +749,32 @@ static int max9286_s_stream(struct v4l2_subdev *sd, int enable)
> >  	return 0;
> >  }
> >
> > +static int max9286_g_frame_interval(struct v4l2_subdev *sd,
> > +				    struct v4l2_subdev_frame_interval *interval)
> > +{
> > +	struct max9286_priv *priv = sd_to_max9286(sd);
> > +
> > +	if (interval->pad == MAX9286_SRC_PAD)
> 
> Ah!
> 
> I would have expected, as this setting applies to all cameras, and
> consequentially to the output image stream frame rate, that the
> operation should have been done on the single source pad... Why is
> this not the case ?

I went back and forth between the two, I think it would work fine on the
source pad as well. I'll give it a try.

> > +		return -EINVAL;
> > +
> > +	interval->interval = priv->interval;
> > +
> > +	return 0;
> > +}
> > +
> > +static int max9286_s_frame_interval(struct v4l2_subdev *sd,
> > +				    struct v4l2_subdev_frame_interval *interval)
> > +{
> > +	struct max9286_priv *priv = sd_to_max9286(sd);
> > +
> > +	if (interval->pad == MAX9286_SRC_PAD)
> > +		return -EINVAL;
> > +
> > +	priv->interval = interval->interval;
> > +
> > +	return 0;
> > +}
> > +
> >  static int max9286_enum_mbus_code(struct v4l2_subdev *sd,
> >  				  struct v4l2_subdev_state *sd_state,
> >  				  struct v4l2_subdev_mbus_code_enum *code)
> > @@ -806,6 +866,8 @@ static int max9286_get_fmt(struct v4l2_subdev *sd,
> >
> >  static const struct v4l2_subdev_video_ops max9286_video_ops = {
> >  	.s_stream	= max9286_s_stream,
> > +	.g_frame_interval = max9286_g_frame_interval,
> > +	.s_frame_interval = max9286_s_frame_interval,
> >  };
> >
> >  static const struct v4l2_subdev_pad_ops max9286_pad_ops = {
> > @@ -998,9 +1060,7 @@ static int max9286_setup(struct max9286_priv *priv)
> >  		      MAX9286_CSILANECNT(priv->csi2_data_lanes) |
> >  		      MAX9286_DATATYPE_YUV422_8BIT);
> >
> > -	/* Automatic: FRAMESYNC taken from the slowest Link. */
> > -	max9286_write(priv, 0x01, MAX9286_FSYNCMODE_INT_HIZ |
> > -		      MAX9286_FSYNCMETH_AUTO);
> > +	max9286_set_fsync_period(priv);
> >
> >  	/* Enable HS/VS encoding, use D14/15 for HS/VS, invert VS. */
> >  	max9286_write(priv, 0x0c, MAX9286_HVEN | MAX9286_INVVS |

-- 
Regards,

Laurent Pinchart