Re: Re: [PATCH 14/19] media: i2c: imx290: Implement HBLANK and VBLANK controls

Dave Stevenson
2022-10-17T13:47:12Z

Hi Laurent

On Sun, 16 Oct 2022 at 07:11, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hello,
>
> On Thu, Jul 21, 2022 at 05:37:23PM +0100, Dave Stevenson wrote:
> > On Thu, 21 Jul 2022 at 12:32, Alexander Stein wrote:
> > > Am Donnerstag, 21. Juli 2022, 13:17:21 CEST schrieb Laurent Pinchart:
> > > > On Thu, Jul 21, 2022 at 12:05:46PM +0200, Alexander Stein wrote:
> > > > > Am Donnerstag, 21. Juli 2022, 10:35:35 CEST schrieb Laurent Pinchart:
> > > > > > Add support for the V4L2_CID_HBLANK and V4L2_CID_VBLANK controls to the
> > > > > > imx290 driver. Make the controls read-only to start with, to report the
> > > > > > values to userspace for timing calculation.
> > > > > >
> > > > > > Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> > > > > > ---
> > > > > >
> > > > > > drivers/media/i2c/imx290.c | 39 +++++++++++++++++++++++++++++++++++++-
> > > > > > 1 file changed, 38 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/media/i2c/imx290.c b/drivers/media/i2c/imx290.c
> > > > > > index 4408dd3e191f..7190399f4111 100644
> > > > > > --- a/drivers/media/i2c/imx290.c
> > > > > > +++ b/drivers/media/i2c/imx290.c
> > > > > > @@ -146,6 +146,8 @@ struct imx290 {
> > > > > > struct v4l2_ctrl_handler ctrls;
> > > > > > struct v4l2_ctrl *link_freq;
> > > > > > struct v4l2_ctrl *pixel_rate;
> > > > > > + struct v4l2_ctrl *hblank;
> > > > > > + struct v4l2_ctrl *vblank;
> > > > > > struct mutex lock;
> > > > > > };
> > > > > >
> > > > > > @@ -642,6 +644,20 @@ static int imx290_set_fmt(struct v4l2_subdev *sd,
> > > > > > if (imx290->pixel_rate)
> > > > > > __v4l2_ctrl_s_ctrl_int64(imx290->pixel_rate,
> > > > > > imx290_calc_pixel_rate(imx290));
> > > > > > +
> > > > > > + if (imx290->hblank) {
> > > > > > + unsigned int hblank = mode->hmax - mode->width;
> > > > > > +
> > > > > > + __v4l2_ctrl_modify_range(imx290->hblank, hblank, hblank,
> > > > > > + 1, hblank);
> > > > > > + }
> > > > > > +
> > > > > > + if (imx290->vblank) {
> > > > > > + unsigned int vblank = IMX290_VMAX_DEFAULT - mode->height;
> > > > > > +
> > > > > > + __v4l2_ctrl_modify_range(imx290->vblank, vblank, vblank,
> > > > > > + 1, vblank);
> > > > > > + }
> > > > > > }
> > > > > >
> > > > > > *format = fmt->format;
> > > > > > @@ -880,9 +896,10 @@ static const struct media_entity_operations imx290_subdev_entity_ops = {
> > > > > >
> > > > > > static int imx290_ctrl_init(struct imx290 *imx290)
> > > > > > {
> > > > > > + unsigned int blank;
> > > > > > int ret;
> > > > > >
> > > > > > - v4l2_ctrl_handler_init(&imx290->ctrls, 5);
> > > > > > + v4l2_ctrl_handler_init(&imx290->ctrls, 7);
> > > > > > imx290->ctrls.lock = &imx290->lock;
> > > > > >
> > > > > > v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
> > > > > > @@ -910,6 +927,26 @@ static int imx290_ctrl_init(struct imx290 *imx290)
> > > > > > ARRAY_SIZE(imx290_test_pattern_menu) - 1,
> > > > > > 0, 0, imx290_test_pattern_menu);
> > > > > >
> > > > > > + /*
> > > > > > + * Horizontal blanking is controlled through the HMAX register, which
> > > > > > + * contains a line length in INCK clock units. The INCK frequency is
> > > > > > + * fixed to 74.25 MHz. The HMAX value is currently fixed to 1100,
> > > > > > + * convert it to a number of pixels based on the nominal pixel rate.
> > > > > > + */
> > > > >
> > > > > Currently the driver only supports 37.125 MHz, please refer to
> > > > > imx290_probe.
> > > >
> > > > Indeed. Re-reading the comment, I suspect something is wrong, as hmax is
> > > > not converted to pixels here (and is also not fixed to 1100).
>
> I'll drop the comment in v2.
>
> > > > The only
> > > > datasheet I found that is publicly accessed doesn't explain very clearly
> > > > how the HMAX value should be computed. Based on your experience with IMX
> > > > sensors, would you be able to shed some light on this ?
> >
> > It is pretty much a standard HTS setting based on a pixel rate that is
> > fixed at 148.5MPix/s.
>
> I'm following you for HTS, but not for the fixed pixel rate. Could you
> elaborate ?

If you work through the numbers you'll find the pixel rate for the
720p mode in the current driver is wrong.

As documented in the datasheet (page 50), the link rate is dropped
from 445.5Mbit/s for 1080p60 in 4 lane mode to 297Mbit/s for 720p60.
The behaviour of the LINK_FREQ control is therefore correct (I've
checked it on an oscilloscope too).

If you look at the HMAX and VMAX numbers for the 720p mode on page 71,
VMAX is 0x2ee (750 decimal), and HMAX is 0x0ce4 (3300 decimal) for
60fps. The driver uses these numbers too in advertising VBLANK and
HBLANK. All good so far.

750 * 3300 * 60(fps) = 148500000, which is the same pixel rate as for
1080p, and not related to the link frequency selected by the mode.
The sensor array can run faster than the CSI block, and
imx290_calc_pixel_rate() is totally bogus.

PIXEL_RATE != LINK_FREQ.

> > Likewise VMAX is equivalent to a traditional VTS.
>
> Yes, that one is easy.
>
> > I've been through the same path in
> > https://github.com/raspberrypi/linux/commits/rpi-5.15.y/drivers/media/i2c/imx290.c
> >
> > > Can you share the link to this datasheet you found?
>
> https://static6.arrow.com/aropdfconversion/c0c7efde6571c768020a72f59b226308b9669e45/sony_imx290lqr-c_datasheet.pdf

Thanks - it's helpful to be able to quote a public source rather than
risk upsetting vendors by quoting their confidential datasheets.

Dave

> > > Sorry, my experience is more like try and error. I don't fully understand this
> > > as well, but apparently this depends on frame rate select (FRSEL).
> >
> > FRSEL is the one difference between IMX327 and IMX290 (and presumably
> > IMX462 too). IMX290 adds "0" as a valid value for 120/100fps mode.
> > However there is no need to change FRSEL for standard frame rate
> > control - you can set it at 0x01 and get a full range of frame rates
> > through VMAX and HMAX. If you wished to extend that range for slower
> > rates, you could conditionally set it to 0x2 to double the frame time.
> >
> > > > > > + blank = imx290->current_mode->hmax - imx290->current_mode->width;
> > > > > > + imx290->hblank = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
> > > > > > + V4L2_CID_HBLANK, blank, blank, 1,
> > > > > > + blank);
> > > > > > + if (imx290->hblank)
> > > > > > + imx290->hblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> > > > > > +
> > > > > > + blank = IMX290_VMAX_DEFAULT - imx290->current_mode->height;
> > > > > > + imx290->vblank = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
> > > > > > + V4L2_CID_VBLANK, blank, blank, 1,
> > > > > > + blank);
> > > > > > + if (imx290->vblank)
> > > > > > + imx290->vblank->flags |= V4L2_CTRL_FLAG_READ_ONLY;
> > > > > > +
> > > > > >
> > > > > > imx290->sd.ctrl_handler = &imx290->ctrls;
> > > > > >
> > > > > > if (imx290->ctrls.error) {
>
> --
> Regards,
>
> Laurent Pinchart