linux-kernel - Re: [Patch v2 1/3] media: ov5640: add PIXEL

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Date:   Thu, 3 Oct 2019 07:07:41 -0500
From:   Benoit Parrot <bparrot@...com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
CC:     Jacopo Mondi <jacopo@...ndi.org>,
        Hans Verkuil <hverkuil@...all.nl>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [Patch v2 1/3] media: ov5640: add PIXEL_RATE control

Sakari Ailus <sakari.ailus@...ux.intel.com> wrote on Thu [2019-Oct-03 10:22:51 +0300]:
> Hi Jacopo, Benoit,
> 
> On Thu, Oct 03, 2019 at 09:17:14AM +0200, Jacopo Mondi wrote:
> > Hi Benoit,
> > 
> > On Wed, Oct 02, 2019 at 08:51:32AM -0500, Benoit Parrot wrote:
> > > Add v4l2 controls to report the pixel rates of each mode. This is
> > > needed by some CSI2 receiver in order to perform proper DPHY
> > > configuration.
> > >
> > > Signed-off-by: Benoit Parrot <bparrot@...com>
> > > ---
> > >  drivers/media/i2c/ov5640.c | 25 +++++++++++++++++++++++++
> > >  1 file changed, 25 insertions(+)
> > >
> > > diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
> > > index 500d9bbff10b..5198dc887400 100644
> > > --- a/drivers/media/i2c/ov5640.c
> > > +++ b/drivers/media/i2c/ov5640.c
> > > @@ -193,6 +193,9 @@ struct ov5640_mode_info {
> > >
> > >  struct ov5640_ctrls {
> > >  	struct v4l2_ctrl_handler handler;
> > > +	struct {
> > > +		struct v4l2_ctrl *pixel_rate;
> > > +	};
> > 
> > Do you need to wrap this v4l2_ctrl in it's own unnamed struct? Other
> > controls here declared in this way are clustered and, if I'm not
> > mistaken, using unnamed struct to wrap them is just a typographically
> > nice way to convey that. I think your new control could be declared
> > without a wrapping struct { }.
> > 
> > >  	struct {
> > >  		struct v4l2_ctrl *auto_exp;
> > >  		struct v4l2_ctrl *exposure;
> > > @@ -2194,6 +2197,16 @@ static int ov5640_try_fmt_internal(struct v4l2_subdev *sd,
> > >  	return 0;
> > >  }
> > >
> > > +static u64 ov5640_calc_pixel_rate(struct ov5640_dev *sensor)
> > > +{
> > > +	u64 rate;
> > > +
> > > +	rate = sensor->current_mode->vtot * sensor->current_mode->htot;
> > > +	rate *= ov5640_framerates[sensor->current_fr];
> > > +
> > > +	return rate;
> > > +}
> > > +
> > 
> > Just to point out this is the -theoretical- pixel rate, and might be
> > quite different from the one calculated by the clock tree tuning
> > procedure (which should be updated to match Hugues' latest findings).
> 
> Hmm. Considering the xclk rate may be pretty much anything, I'd suppose
> the value above would only be correct for a given xclk rate.

I am not sure about that, different xclk rate might yield slightly
different byte clock, but all in all the resolution and framerate pretty
much dictate the end result, no?

> 
> Could this be simply calculated from the clock tree configuration, to get
> the right value in all cases?

It probably could, and as I said earlier I gave it a try and failed, since
the theoretical value worked for me that's what I went with. Those are the
same values that Maxime's patch referred to. (dfbfb7aa832cdb media: ov5640:
Compute the clock rate at runtime).

Here I am just "publishing it".

Benoit

> 
> > 
> > >  static int ov5640_set_fmt(struct v4l2_subdev *sd,
> > >  			  struct v4l2_subdev_pad_config *cfg,
> > >  			  struct v4l2_subdev_format *format)
> > > @@ -2233,6 +2246,8 @@ static int ov5640_set_fmt(struct v4l2_subdev *sd,
> > >  	if (mbus_fmt->code != sensor->fmt.code)
> > >  		sensor->pending_fmt_change = true;
> > >
> > > +	__v4l2_ctrl_s_ctrl_int64(sensor->ctrls.pixel_rate,
> > > +				 ov5640_calc_pixel_rate(sensor));
> > >  out:
> > >  	mutex_unlock(&sensor->lock);
> > >  	return ret;
> > > @@ -2657,6 +2672,13 @@ static int ov5640_init_controls(struct ov5640_dev *sensor)
> > >  	/* we can use our own mutex for the ctrl lock */
> > >  	hdl->lock = &sensor->lock;
> > >
> > > +	/* Clock related controls */
> > > +	ctrls->pixel_rate =
> > > +		v4l2_ctrl_new_std(hdl, ops,
> > 
> > If you like it better, this could fit in 1 line
> > 
> > 	ctrls->pixel_rate = v4l2_ctrl_new_std(hdl, ops, V4L2_CID_PIXEL_RATE,
> > 					      0, INT_MAX, 1,
> > 					      ov5640_calc_pixel_rate(sensor)
> > 
> > Thanks
> >    j
> > 
> > > +				  V4L2_CID_PIXEL_RATE, 0, INT_MAX, 1,
> > > +				  ov5640_calc_pixel_rate(sensor));
> > 
> > 
> > > +	ctrls->pixel_rate->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> 
> Note that ctrls->pixel_rate is NULL if e.g. memory allocation fails when
> creating the control.
> 
> > > +
> > >  	/* Auto/manual white balance */
> > >  	ctrls->auto_wb = v4l2_ctrl_new_std(hdl, ops,
> > >  					   V4L2_CID_AUTO_WHITE_BALANCE,
> > > @@ -2816,6 +2838,9 @@ static int ov5640_s_frame_interval(struct v4l2_subdev *sd,
> > >  		sensor->frame_interval = fi->interval;
> > >  		sensor->current_mode = mode;
> > >  		sensor->pending_mode_change = true;
> > > +
> > > +		__v4l2_ctrl_s_ctrl_int64(sensor->ctrls.pixel_rate,
> > > +					 ov5640_calc_pixel_rate(sensor));
> > >  	}
> > >  out:
> > >  	mutex_unlock(&sensor->lock);
> 
> -- 
> Regards,
> 
> Sakari Ailus
> sakari.ailus@...ux.intel.com