[RFC v3 2/2] media: staging: rkisp1: allow quantization conversion from userspace for isp source pad
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Sun Jun 28 17:37:35 EDT 2020
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 at collabora.com> 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 at collabora.com>
> >>>>>>>>>>>>>> ---
> >>>>>>>>>>>>>> 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 at ragnatech.se>
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 at ideasonboard.com>
Date: Fri Apr 24 15:43:31 2020 +0200
media: v4l2: Extend VIDIOC_ENUM_FMT to support MC-centric devices
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.
--
Regards,
Laurent Pinchart
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