Re: [RFC v3 2/2] media: staging: rkisp1: allow quantization conversion from userspace for isp source pad

[Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx>]

On 28.06.20 23:37, Laurent Pinchart wrote:
> Hi Tomasz,
>
> On Sun, Jun 28, 2020 at 11:33:30PM +0200, Tomasz Figa wrote:
> > On Sun, Jun 28, 2020 at 10:27 PM Laurent Pinchart wrote:
> > > On Sun, Jun 28, 2020 at 04:59:34PM +0200, Tomasz Figa wrote:
> > > > On Sun, Jun 28, 2020 at 3:15 PM Laurent Pinchart wrote:
> > > > > On Sun, Jun 28, 2020 at 03:10:41PM +0200, Tomasz Figa wrote:
> > > > > > On Fri, Jun 26, 2020 at 2:15 AM Helen Koike <helen.koike@xxxxxxxxxxxxx> wrote:
> > > > > > > On 6/18/20 4:25 PM, Tomasz Figa wrote:
> > > > > > > > On Thu, Jun 18, 2020 at 08:54:34PM +0200, Dafna Hirschfeld wrote:
> > > > > > > > > On 18.06.20 20:49, Tomasz Figa wrote:
> > > > > > > > > > On Thu, Jun 18, 2020 at 08:26:33PM +0200, Dafna Hirschfeld wrote:
> > > > > > > > > > > On 18.06.20 19:27, Tomasz Figa wrote:
> > > > > > > > > > > > On Wed, Jun 10, 2020 at 2:08 PM Tomasz Figa wrote:
> > > > > > > > > > > > > On Thu, Jun 4, 2020 at 9:11 PM Dafna Hirschfeld wrote:
> > > > > > > > > > > > > > On 04.06.20 19:54, Tomasz Figa wrote:
> > > > > > > > > > > > > > > On Thu, Apr 16, 2020 at 04:56:05PM +0200, Dafna Hirschfeld wrote:
> > > > > > > > > > > > > > > > The isp entity has a hardware support to force full range quantization
> > > > > > > > > > > > > > > > for YUV formats. Use the new API to indicate userspace that
> > > > > > > > > > > > > > > > quantization conversion is supported by adding the flag
> > > > > > > > > > > > > > > > V4L2_SUBDEV_MBUS_CODE_CSC_QUANTIZATION during media code enumeration.
> > > > > > > > > > > > > > > > Then uppon s_fmt on the video source pad, we assign the
> > > > > > > > > > > > > > > > quantization from userspace for YUV formats.
> > > > > > > > > > > > > > > > Also in the capture and resizer entities we retrieve the colorspace
> > > > > > > > > > > > > > > > from the isp entity.
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@xxxxxxxxxxxxx>
> > > > > > > > > > > > > > > > ---
> > > > > > > > > > > > > > > >      drivers/staging/media/rkisp1/rkisp1-capture.c | 28 ++++++-------
> > > > > > > > > > > > > > > >      drivers/staging/media/rkisp1/rkisp1-common.h  |  2 +
> > > > > > > > > > > > > > > >      drivers/staging/media/rkisp1/rkisp1-isp.c     | 39 +++++++++++++++++--
> > > > > > > > > > > > > > > >      drivers/staging/media/rkisp1/rkisp1-resizer.c | 13 +++++++
> > > > > > > > > > > > > > > >      4 files changed, 65 insertions(+), 17 deletions(-)
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > diff --git a/drivers/staging/media/rkisp1/rkisp1-capture.c b/drivers/staging/media/rkisp1/rkisp1-capture.c
> > > > > > > > > > > > > > > > index fbf62399fe3d..aca0f93bc772 100644
> > > > > > > > > > > > > > > > --- a/drivers/staging/media/rkisp1/rkisp1-capture.c
> > > > > > > > > > > > > > > > +++ b/drivers/staging/media/rkisp1/rkisp1-capture.c
> > > > > > > > > > > > > > > > @@ -1066,14 +1066,13 @@ static void rkisp1_try_fmt(const struct rkisp1_capture *cap,
> > > > > > > > > > > > > > > >                            const struct v4l2_format_info **fmt_info)
> > > > > > > > > > > > > > > >      {
> > > > > > > > > > > > > > > >         const struct rkisp1_capture_config *config = cap->config;
> > > > > > > > > > > > > > > > -    struct rkisp1_capture *other_cap =
> > > > > > > > > > > > > > > > -                    &cap->rkisp1->capture_devs[cap->id ^ 1];
> > > > > > > > > > > > > > > >         const struct rkisp1_capture_fmt_cfg *fmt;
> > > > > > > > > > > > > > > >         const struct v4l2_format_info *info;
> > > > > > > > > > > > > > > >         const unsigned int max_widths[] = { RKISP1_RSZ_MP_SRC_MAX_WIDTH,
> > > > > > > > > > > > > > > >                                             RKISP1_RSZ_SP_SRC_MAX_WIDTH };
> > > > > > > > > > > > > > > >         const unsigned int max_heights[] = { RKISP1_RSZ_MP_SRC_MAX_HEIGHT,
> > > > > > > > > > > > > > > >                                              RKISP1_RSZ_SP_SRC_MAX_HEIGHT};
> > > > > > > > > > > > > > > > +    struct v4l2_subdev_format isp_sd_fmt;
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         fmt = rkisp1_find_fmt_cfg(cap, pixm->pixelformat);
> > > > > > > > > > > > > > > >         if (!fmt) {
> > > > > > > > > > > > > > > > @@ -1081,24 +1080,27 @@ static void rkisp1_try_fmt(const struct rkisp1_capture *cap,
> > > > > > > > > > > > > > > >                 pixm->pixelformat = fmt->fourcc;
> > > > > > > > > > > > > > > >         }
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +    rkisp1_get_isp_src_fmt(cap->rkisp1, &isp_sd_fmt);
> > > > > > > > > > > > > > > > +    pixm->field = isp_sd_fmt.format.field;
> > > > > > > > > > > > > > > > +    pixm->colorspace = isp_sd_fmt.format.colorspace;
> > > > > > > > > > > > > > > > +    pixm->ycbcr_enc = isp_sd_fmt.format.ycbcr_enc;
> > > > > > > > > > > > > > > > +    pixm->xfer_func = isp_sd_fmt.format.xfer_func;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +    /*
> > > > > > > > > > > > > > > > +     * isp has a feature to set full range quantization for yuv formats.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > How about "select between limited and full range for YUV formats"?
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +     * so we need to get the format from the isp.
> > > > > > > > > > > > > > > > +     */
> > > > > > > > > > > > > > > > +    pixm->quantization = isp_sd_fmt.format.quantization;
> > > > > > > > > > > > > > > > +    if (!v4l2_is_format_yuv(cap->pix.info))
> > > > > > > > > > > > > > > > +            pixm->quantization = V4L2_QUANTIZATION_FULL_RANGE;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >         pixm->width = clamp_t(u32, pixm->width,
> > > > > > > > > > > > > > > >                               RKISP1_RSZ_SRC_MIN_WIDTH, max_widths[cap->id]);
> > > > > > > > > > > > > > > >         pixm->height = clamp_t(u32, pixm->height,
> > > > > > > > > > > > > > > >                                RKISP1_RSZ_SRC_MIN_HEIGHT, max_heights[cap->id]);
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > -    pixm->field = V4L2_FIELD_NONE;
> > > > > > > > > > > > > > > > -    pixm->colorspace = V4L2_COLORSPACE_DEFAULT;
> > > > > > > > > > > > > > > > -    pixm->ycbcr_enc = V4L2_YCBCR_ENC_DEFAULT;
> > > > > > > > > > > > > > > > -
> > > > > > > > > > > > > > > >         info = rkisp1_fill_pixfmt(pixm, cap->id);
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > -    /* can not change quantization when stream-on */
> > > > > > > > > > > > > > > > -    if (other_cap->is_streaming)
> > > > > > > > > > > > > > > > -            pixm->quantization = other_cap->pix.fmt.quantization;
> > > > > > > > > > > > > > > > -    /* output full range by default, take effect in params */
> > > > > > > > > > > > > > > > -    else if (!pixm->quantization ||
> > > > > > > > > > > > > > > > -             pixm->quantization > V4L2_QUANTIZATION_LIM_RANGE)
> > > > > > > > > > > > > > > > -            pixm->quantization = V4L2_QUANTIZATION_FULL_RANGE;
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         if (fmt_cfg)
> > > > > > > > > > > > > > > >                 *fmt_cfg = fmt;
> > > > > > > > > > > > > > > > diff --git a/drivers/staging/media/rkisp1/rkisp1-common.h b/drivers/staging/media/rkisp1/rkisp1-common.h
> > > > > > > > > > > > > > > > index 2d7b7e078636..7a5576fa14c9 100644
> > > > > > > > > > > > > > > > --- a/drivers/staging/media/rkisp1/rkisp1-common.h
> > > > > > > > > > > > > > > > +++ b/drivers/staging/media/rkisp1/rkisp1-common.h
> > > > > > > > > > > > > > > > @@ -300,6 +300,8 @@ int rkisp1_isp_register(struct rkisp1_device *rkisp1,
> > > > > > > > > > > > > > > >                         struct v4l2_device *v4l2_dev);
> > > > > > > > > > > > > > > >      void rkisp1_isp_unregister(struct rkisp1_device *rkisp1);
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +int rkisp1_get_isp_src_fmt(struct rkisp1_device *rkisp1,
> > > > > > > > > > > > > > > > +                       struct v4l2_subdev_format *sd_fmt);
> > > > > > > > > > > > > > > >      const struct rkisp1_isp_mbus_info *rkisp1_isp_mbus_info_get(u32 mbus_code);
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >      irqreturn_t rkisp1_isp_isr(struct rkisp1_device *rkisp1);
> > > > > > > > > > > > > > > > diff --git a/drivers/staging/media/rkisp1/rkisp1-isp.c b/drivers/staging/media/rkisp1/rkisp1-isp.c
> > > > > > > > > > > > > > > > index dee8e96f3900..6fdf5ed0b6b1 100644
> > > > > > > > > > > > > > > > --- a/drivers/staging/media/rkisp1/rkisp1-isp.c
> > > > > > > > > > > > > > > > +++ b/drivers/staging/media/rkisp1/rkisp1-isp.c
> > > > > > > > > > > > > > > > @@ -613,6 +613,10 @@ static int rkisp1_isp_enum_mbus_code(struct v4l2_subdev *sd,
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >                 if (code->index == pos - 1) {
> > > > > > > > > > > > > > > >                         code->code = fmt->mbus_code;
> > > > > > > > > > > > > > > > +                    if (fmt->pixel_enc == V4L2_PIXEL_ENC_YUV &&
> > > > > > > > > > > > > > > > +                        dir == RKISP1_DIR_SRC)
> > > > > > > > > > > > > > > > +                            code->flags =
> > > > > > > > > > > > > > > > +                                    V4L2_SUBDEV_MBUS_CODE_CSC_QUANTIZATION;
> > > > > > > > > > > > > > > >                         return 0;
> > > > > > > > > > > > > > > >                 }
> > > > > > > > > > > > > > > >         }
> > > > > > > > > > > > > > > > @@ -639,12 +643,21 @@ static int rkisp1_isp_init_config(struct v4l2_subdev *sd,
> > > > > > > > > > > > > > > >         sink_crop->height = RKISP1_DEFAULT_HEIGHT;
> > > > > > > > > > > > > > > >         sink_crop->left = 0;
> > > > > > > > > > > > > > > >         sink_crop->top = 0;
> > > > > > > > > > > > > > > > +    sink_fmt->colorspace = V4L2_COLORSPACE_SRGB;
> > > > > > > > > > > > > > > > +    sink_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(sink_fmt->colorspace);
> > > > > > > > > > > > > > > > +    sink_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(sink_fmt->colorspace);
> > > > > > > > > > > > > > > > +    sink_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         src_fmt = v4l2_subdev_get_try_format(sd, cfg,
> > > > > > > > > > > > > > > >                                              RKISP1_ISP_PAD_SOURCE_VIDEO);
> > > > > > > > > > > > > > > >         *src_fmt = *sink_fmt;
> > > > > > > > > > > > > > > >         src_fmt->code = RKISP1_DEF_SRC_PAD_FMT;
> > > > > > > > > > > > > > > > -    src_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
> > > > > > > > > > > > > > > > +    src_fmt->colorspace = V4L2_COLORSPACE_SRGB;
> > > > > > > > > > > > > > > > +    src_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(src_fmt->colorspace);
> > > > > > > > > > > > > > > > +    src_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(src_fmt->colorspace);
> > > > > > > > > > > > > > > > +    src_fmt->quantization = V4L2_QUANTIZATION_LIM_RANGE;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         src_crop = v4l2_subdev_get_try_crop(sd, cfg,
> > > > > > > > > > > > > > > >                                             RKISP1_ISP_PAD_SOURCE_VIDEO);
> > > > > > > > > > > > > > > > @@ -687,10 +700,17 @@ static void rkisp1_isp_set_src_fmt(struct rkisp1_isp *isp,
> > > > > > > > > > > > > > > >                 isp->src_fmt = mbus_info;
> > > > > > > > > > > > > > > >         src_fmt->width  = src_crop->width;
> > > > > > > > > > > > > > > >         src_fmt->height = src_crop->height;
> > > > > > > > > > > > > > > > -    src_fmt->quantization = format->quantization;
> > > > > > > > > > > > > > > > -    /* full range by default */
> > > > > > > > > > > > > > > > -    if (!src_fmt->quantization)
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +    src_fmt->colorspace = V4L2_COLORSPACE_SRGB;
> > > > > > > > > > > > > > > > +    src_fmt->ycbcr_enc = V4L2_MAP_YCBCR_ENC_DEFAULT(src_fmt->colorspace);
> > > > > > > > > > > > > > > > +    src_fmt->xfer_func = V4L2_MAP_XFER_FUNC_DEFAULT(src_fmt->colorspace);
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +    if (mbus_info->pixel_enc == V4L2_PIXEL_ENC_BAYER)
> > > > > > > > > > > > > > > >                 src_fmt->quantization = V4L2_QUANTIZATION_FULL_RANGE;
> > > > > > > > > > > > > > > > +    else if (format->quantization == V4L2_QUANTIZATION_DEFAULT)
> > > > > > > > > > > > > > > > +            src_fmt->quantization = V4L2_QUANTIZATION_LIM_RANGE;
> > > > > > > > > > > > > > > > +    else
> > > > > > > > > > > > > > > > +            src_fmt->quantization = format->quantization;
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         *format = *src_fmt;
> > > > > > > > > > > > > > > >      }
> > > > > > > > > > > > > > > > @@ -1068,6 +1088,17 @@ int rkisp1_isp_register(struct rkisp1_device *rkisp1,
> > > > > > > > > > > > > > > >         return ret;
> > > > > > > > > > > > > > > >      }
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +int rkisp1_get_isp_src_fmt(struct rkisp1_device *rkisp1,
> > > > > > > > > > > > > > > > +                       struct v4l2_subdev_format *sd_fmt)
> > > > > > > > > > > > > > > > +{
> > > > > > > > > > > > > > > > +    struct rkisp1_isp *isp = &rkisp1->isp;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +    sd_fmt->which = V4L2_SUBDEV_FORMAT_ACTIVE;
> > > > > > > > > > > > > > > > +    sd_fmt->pad = RKISP1_ISP_PAD_SOURCE_VIDEO;
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > > +    return v4l2_subdev_call(&isp->sd, pad, get_fmt, NULL, sd_fmt);
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Do we need to get through the external API to access data that is
> > > > > > > > > > > > > > > driver-internal anyway?
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +}
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > > >      void rkisp1_isp_unregister(struct rkisp1_device *rkisp1)
> > > > > > > > > > > > > > > >      {
> > > > > > > > > > > > > > > >         struct v4l2_subdev *sd = &rkisp1->isp.sd;
> > > > > > > > > > > > > > > > diff --git a/drivers/staging/media/rkisp1/rkisp1-resizer.c b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> > > > > > > > > > > > > > > > index 7b6b7ddd4169..8705b133de68 100644
> > > > > > > > > > > > > > > > --- a/drivers/staging/media/rkisp1/rkisp1-resizer.c
> > > > > > > > > > > > > > > > +++ b/drivers/staging/media/rkisp1/rkisp1-resizer.c
> > > > > > > > > > > > > > > > @@ -525,6 +525,7 @@ static void rkisp1_rsz_set_sink_fmt(struct rkisp1_resizer *rsz,
> > > > > > > > > > > > > > > >         const struct rkisp1_isp_mbus_info *mbus_info;
> > > > > > > > > > > > > > > >         struct v4l2_mbus_framefmt *sink_fmt, *src_fmt;
> > > > > > > > > > > > > > > >         struct v4l2_rect *sink_crop;
> > > > > > > > > > > > > > > > +    struct v4l2_subdev_format isp_sd_fmt;
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > >         sink_fmt = rkisp1_rsz_get_pad_fmt(rsz, cfg, RKISP1_RSZ_PAD_SINK, which);
> > > > > > > > > > > > > > > >         src_fmt = rkisp1_rsz_get_pad_fmt(rsz, cfg, RKISP1_RSZ_PAD_SRC, which);
> > > > > > > > > > > > > > > > @@ -539,8 +540,20 @@ static void rkisp1_rsz_set_sink_fmt(struct rkisp1_resizer *rsz,
> > > > > > > > > > > > > > > >         if (which == V4L2_SUBDEV_FORMAT_ACTIVE)
> > > > > > > > > > > > > > > >                 rsz->pixel_enc = mbus_info->pixel_enc;
> > > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > > +    rkisp1_get_isp_src_fmt(rsz->rkisp1, &isp_sd_fmt);
> > > > > > > > > > > > > > > > +
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Is this necessary? My understanding was that in the subdev model, it was
> > > > > > > > > > > > > > > the userspace responsibility to propagate any configuration changes through
> > > > > > > > > > > > > > > the graph.
> > > > > > > > > > > > > > >
> > > > > > > > > > > > > > > Also, doing this only here wouldn't fully maintain the
> > > > > > > > > > > > > > > consistency of the state. For example, if one sets the ISP subdev format
> > > > > > > > > > > > > > > first, then the resizer subdev and then the ISP subdev again, wouldn't the
> > > > > > > > > > > > > > > resizer subdev end up with a wrong format?
> > > > > > > > > > > > > >
> > > > > > > > > > > > > > yes, this is indeed a bug, I am preparing v4 now.
> > > > > > > > > > > > > > What I thought to do is adding quantization conversion
> > > > > > > > > > > > > > support also on ther resizer and capture entities.
> > > > > > > > > > > > > > Then in the 'link_validation' callbacks, there
> > > > > > > > > > > > > > is a validation that the quantization fields matches.
> > > > > > > > > > > > >
> > > > > > > > > > > > > My understanding is that, if we have the following topology
> > > > > > > > > > > > >
> > > > > > > > > > > > > [ ISP ] -> [ Resizer ] -> [ Video node ]
> > > > > > > > > > > > >
> > > > > > > > > > > > > then the ISP source pad would have the csc capability, while resizer
> > > > > > > > > > > > > and video node would just accept whatever is configured on their sink
> > > > > > > > > > > > > pads (no need for csc capability for that) and propagate that to their
> > > > > > > > > > > > > outputs, i.e. resizer source pad and video node CAPTURE format.
> > > > > > > > > > > > >
> > > > > > > > > > > > > Is this what you were going to implement?
> > > > > > > > > > > Hi, I sent a v4 where the CSC capability is set on the reiszer and capture as well.
> > > > > > > > > > > I can send a v5 implementing it the way you suggest. Currently the doc says that the colorspace fields
> > > > > > > > > > > must be set by the driver for capture streams. This implies that userspace can set it
> > > > > > > > > > > only if the CSC is supported.
> > > > > > > > > >
> > > > > > > > > > Why would the userspace have to set it for the capture stream on the
> > > > > > > > > > resizer and video nodes? Couldn't the userspace set it to DEFAULT and
> > > > > > > > > > then the driver override to whatever it received on the corresponding
> > > > > > > > > > sink?
> > > > > > >
> > > > > > > According to the documentation [1]:
> > > > > > >
> > > > > > > "the default quantization encoding as defined by the colorspace"
> > > > > > >
> > > > > > > Then, for instance, the default for V4L2_COLORSPACE_SRGB is limited range [2].
> > > > > > >
> > > > > > > Unless we change the definition of DEFAULT to let it accept whatever it receives on the corresponding sink.
> > > > > > >
> > > > > > > Then the way I understand is:
> > > > > > >
> > > > > > > [sensor]->[isp]->[resizer]->[capture]
> > > > > > >
> > > > > > > Userspace should set quantization on:
> > > > > > > * sensor source pad
> > > > > > > * isp sink pad
> > > > > > > * resizer sink pad
> > > > > > > * capture node
> > > > > > >
> > > > > > > The remaining source pads would get values propagated from their sink pads.
> > > > > > >
> > > > > > > [1] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/colorspaces-defs.html#c.v4l2_quantization
> > > > > > > [2] https://linuxtv.org/downloads/v4l-dvb-apis-new/userspace-api/v4l/colorspaces-details.html#col-srgb
> > > > > >
> > > > > > After discussing this offline, we concluded that:
> > > > > > - only the source pad of the ISP entity should expose the CSC capability,
> > > > > > - the CAPTURE video node should expose only the formats/color spaces
> > > > > > compatible with the current setting of the resizer source,
> > > > > > - consistency between the resizer source format and CAPTURE format
> > > > > > should be implicitly maintained by the driver.
> > > > >
> > > > > Do you mean it should be validated at streamon time ?
> > > >
> > > > Nope. Any V4L2 state must be kept valid all the time, as mandated by
> > > > the general V4L2 principles. Wrong configuration of the video node
> > > > must not be a reason for STREAMON failing.
> > >
> > > That's a wrong interpretation of V4L2. On a video-node-centric device (a
> > > device that doesn't use the subdev userspace API for configuration) this
> > > is correct. In a MC-centric device, the video node and its connected
> > > subdev are configured separately.
> >
> > I don't see this documented anywhere in the specification, maybe
> > except a mention of EPIPE or ENOLINK being returned from STREAMON, but
> > they explicitly refer to pipeline configuration and not a conflict
> > between V4L2 and MC state.
>
> We're suffering from a lack of documentation in this area :-( Niklas has
> authored
>
> commit f645e6256bd1b12523b759fcc610861fb21c24c7
> Author: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> Date:   Tue Apr 21 15:57:38 2020 +0200
>
>      media: v4l2-dev/ioctl: Add V4L2_CAP_IO_MC
>
> which is a first step, now we need to document the behaviour of all
> ioctls properly when the MC and !MC cases differ.
>
> > The behavior as you're suggesting would be at least confusing for the
> > userspace, because it breaks one of the core principles of V4L2 and
> > also there is even no facility to allow the userspace handle this kind
> > of behavior, e.g. how to know which memory formats are supported for
> > given mbus formats of the related sink.
>
> commit e5b6b07a1b45dd9d19bec1fa1d60750b0fcf2fb0
> Author: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> Date:   Fri Apr 24 15:43:31 2020 +0200
>
>      media: v4l2: Extend VIDIOC_ENUM_FMT to support MC-centric devices

Hi,
What if the video device entity wants to support V4L2_CAP_IO_MC and has two
pads registered to the media controller?
It seems to be undefined in the documentation.

Thanks,
Dafna

> Been missing for a long time... I realized that when I started using the
> API in a real userspace implementation instead of just writing test
> tools or very device-specific code that could hardcode all this
> knowledge.
>
> > > > > In MC-based
> > > > > drivers, entities are isolated from each other from a configuration
> > > > > point of view, and the validity of the configuration across the whole
> > > > > pipeline is checked at streamon time. I don't think CSC parameters
> > > > > should be treated differently than formats in this regard.
> > > >
> > > > Indeed, the ISP entity and the resizer entity are isolated from each
> > > > other and they need to be validated separately. However, the resizer
> > > > entity is not isolated from the video node, as there is no
> > > > configuration exposed for the video node in the MC API. If MC exposed
> > > > an explicit format control for the video interface sink pad, then the
> > > > resizer would have to be validated separately indeed, but still that
> > > > video interface sink pad would be tied to the rest of the
> > > > configuration of the video node (e.g. the CAPTURE format).
> > > >
> > > > > > Below is the rationale for that:
> > > > > > - In the MC model, the video node represents the DMA alone (and thus
> > > > > > the reason to have the resizer entities at all) and since the
> > > > > > colorspace is not a property of the DMA, it doesn't belong there.
> > > > > > - Even if we put that aside, both MP and SP can only output the same
> > > > > > colorspace, which would create a dependency between the configuration
> > > > > > of the two video nodes, which is not something well defined by V4L2.
> > > > > > - A video interface in the MC API doesn't expose control over its
> > > > > > input format, which means that the relation between the other side of
> > > > > > the link (resizer source) and the video node is implicit and needs to
> > > > > > be handled internally in the driver.
> > > > > > - V4L2, as opposed to MC, requires that the current state is always
> > > > > > consistent and valid. In this case it means that an ioctl on the video
> > > > > > node must not be able to alter the state in a way that would make it
> > > > > > inconsistent with the state of the matching resizer source.