On Tuesday, October 04, 2011 07:31:27 Mauro Carvalho Chehab wrote:
> Em 03-10-2011 19:37, Javier Martinez Canillas escreveu:
> > Hello,
> >
> > Reading the last emails I understand that still isn't a consensus on
> > the way this has to be made.
>
> True.
>
> > If it has to be implemented at the video
> > device node level or at the sub-device level. And if it has to be made
> > in kernel or user-space.
>
> For now, I propose you to just add/improve the auto-detection on the
> existing callbacks. We need to reach a consensus before working at the pad level.
I agree.
> > On Mon, Oct 3, 2011 at 11:56 PM, Mauro Carvalho Chehab
> > <mchehab@xxxxxxxxxxxxx> wrote:
> >> Em 03-10-2011 18:44, Laurent Pinchart escreveu:
> >>> Hi Mauro,
> >>>
> >>> On Monday 03 October 2011 21:16:45 Mauro Carvalho Chehab wrote:
> >>>> Em 03-10-2011 08:53, Laurent Pinchart escreveu:
> >>>>> On Monday 03 October 2011 11:53:44 Javier Martinez Canillas wrote:
> >>>>>
> >>>>> [snip]
> >>>>>
> >>>>>> Laurent, I have a few questions about MCF and the OMAP3ISP driver if
> >>>>>> you are so kind to answer.
> >>>>>>
> >>>>>> 1- User-space programs that are not MCF aware negotiate the format
> >>>>>> with the V4L2 device (i.e: OMAP3 ISP CCDC output), which is a sink
> >>>>>> pad. But the real format is driven by the analog video format in the
> >>>>>> source pad (i.e: tvp5151).
> >>>>>
> >>>>> That's not different from existing systems using digital sensors, where
> >>>>> the format is driven by the sensor.
> >>>>>
> >>>>>> I modified the ISP driver to get the data format from the source pad
> >>>>>> and set the format for each pad on the pipeline accordingly but I've
> >>>>>> read from the documentation [1] that is not correct to propagate a
> >>>>>> data format from source pads to sink pads, that the correct thing is
> >>>>>> to do it from sink to source.
> >>>>>>
> >>>>>> So, in this case an administrator has to externally configure the
> >>>>>> format for each pad and to guarantee a coherent format on the whole
> >>>>>> pipeline?.
> >>>>>
> >>>>> That's correct (except you don't need to be an administrator to do so
> >>>>> :-)).
> >>>>
> >>>> NACK.
> >>>
> >>> Double NACK :-D
> >>>
> >>>> When userspace sends a VIDIOC_S_STD ioctl to the sink node, the subdevs
> >>>> that are handling the video/audio standard should be changed, in order to
> >>>> obey the V4L2 ioctl. This is what happens with all other drivers since the
> >>>> beginning of the V4L1 API. There's no reason to change it, and such change
> >>>> would be a regression.
> >>>
> >>> The same could have been told for the format API:
> >>>
> >>> "When userspace sends a VIDIOC_S_FMT ioctl to the sink node, the subdevs that
> >>> are handling the video format should be changed, in order to obey the V4L2
> >>> ioctl. This is what happens with all other drivers since the beginning of the
> >>> V4L1 API. There's no reason to change it, and such change would be a
> >>> regression."
> >>>
> >>> But we've introduced a pad-level format API. I don't see any reason to treat
> >>> standard differently.
> >>
> >> Neither do I. The pad-level API should not replace the V4L2 API for standard,
> >> for controls and/or for format settings.
Remember we are talking about the subdev driver here. It makes no sense to
have both a s_mbus_fmt video op and a set_fmt pad op, which both do the same
thing. Bridge drivers should be adapted to use set_fmt only, so we can drop
s_mbus_fmt.
BTW, the names 'set_fmt' and 'get_fmt' are very confusing to me. I always think
these refer to v4l2_format. Can we please rename this to g/s_mbus_fmt? And
set/get_crop to s/g_crop? This for consistent naming.
When it comes to S_STD I don't see the need for a pad version of this. It is
an op that is used to configure subdevs to handle a specific standard. If you
are configuring the pipelines manually, then after calling S_STD you have to
set up the mbus formats yourself.
Of course, I can generate scenarios where you would need to set the standard
through the subdev node (i.e. two video receivers connected to a SoC, one
receiving PAL, the other receiving NTSC, and both streams composed into a single
new stream that's DMA-ed to memory), but frankly, those scenarios are very
contrived :-)
The preset ioctls would be more realistic since I know that a scenario like the
one above does exist for e.g. HDMI inputs, where each can receive a different
format.
In that case the preset ioctls would have to be exposed to the subdev nodes,
allowing you to set it up for each HDMI receiver independently. But you still
do not need pads to do this since this is a subdev-level operation, not pad-level.
> >>
> >>>>>> Or does exist a way to do this automatic?. i.e: The output entity on the
> >>>>>> pipeline promotes the capabilities of the source pad so applications can
> >>>>>> select a data format and this format gets propagated all over the
> >>>>>> pipeline from the sink pad to the source?
> >>>>>
> >>>>> It can be automated in userspace (through a libv4l plugin for instance),
> >>>>> but it's really not the kernel's job to do so.
> >>>>
> >>>> It is a kernel job to handle VIDIOC_S_STD, and not a task to be left to any
> >>>> userspace plugin.
> >>>
> >>> And VIDIOC_S_FMT is handled by userspace for the OMAP3 ISP today. Why are
> >>> standards different ?
> >>
> >> All v4l media devices have sub-devices with either tv decoders or sensors connected
> >> into a sink. The sink implements the /dev/video? node.
> >> When an ioctl is sent to the v4l node, the sensors/decoders are controlled
> >> to implement whatever is requested: video standards, formats etc.
> >>
> >> Changing it would be a major regression. If OMAP3 is not doing the right thing,
> >> it should be fixed, and not the opposite.
> >>
> >
> > That is the approach we took, we hack the isp v4l2 device driver
> > (ispvideo) to bypass the ioctls to the sub-device that as the source
> > pad (tvp5151 in our case, but it could be a sensor as well). So, for
> > example the VIDIOC_S_STD ioctl handler looks like this (I post a
> > simplified version of the code, just to give an idea):
> >
> > static int isp_video_s_std(struct file *file, void *fh, v4l2_std_id *norm)
> > {
> > struct isp_video *video = video_drvdata(file);
> > struct v4l2_subdev *sink_subdev;
> > struct v4l2_subdev *source_subdev;
> >
> > sink_subdev = isp_video_remote_subdev(video, NULL);
> > sink_pad = &sink_subdev->entity.pads[0];
> > source_pad = media_entity_remote_source(sink_pad);
> > source_subdev = media_entity_to_v4l2_subdev(source_pad->entity);
> > v4l2_subdev_call(source_subdev, core, s_std, NULL, norm);
> > }
> >
> > So applications interact with the /dev/video? via V4L2 ioctls whose
> > handlers call the sub-dev functions. Is that what you propose?
>
> Something like that. For example:
>
> static int vidioc_s_std(struct file *file, void *priv, v4l2_std_id *norm)
> {
> /* Do some sanity test/resolution adjustments, etc */
>
> v4l2_device_call_all(&dev->v4l2_dev, 0, core, s_std, dev->norm);
>
> return 0;
> }
>
> It should be noticed that:
>
> 1) a full standard auto-detection is only possible at the V4L2 level, as a
> standard is a composition of audio and video carriers. I intend to work tomorrow
> to add audio auto-detection to pvrusb2;
>
> 2) a full s_std should not only adjust the TV demod pad, but also, the audio pad
> and the tuner pad (if the analog input comes from a tuner).
>
> >> The MC/subdev API is there to fill the blanks, e. g. to handle cases where the
> >> same function could be implemented on two different places of the pipeline, e. g.
> >> when both the sensor and the bridge could do scaling, and userspace wants to
> >> explicitly use one, or the other, but it were never meant to replace the V4L2
> >> functionality.
> >>
> >>>
> >>>>>> [1]: http://linuxtv.org/downloads/v4l-dvb-apis/subdev.html
> >>>>>>
> >>>>>> 2- If the application want a different format that the default
> >>>>>> provided by the tvp5151, (i.e: 720x576 for PAL), where do I have to
> >>>>>> crop the image? I thought this can be made using the CCDC, copying
> >>>>>> less lines to memory or the RESIZER if the application wants a bigger
> >>>>>> image. What is the best approach for this?
> >>>>
> >>>> Not sure if I understood your question, but maybe you're mixing two
> >>>> different concepts here.
> >>>>
> >>>> If the application wants a different image resolution, it will use S_FMT.
> >>>> In this case, what userspace expects is that the driver will scale,
> >>>> if supported, or return -EINVAL otherwise.
> >>>
> >>> With the OMAP3 ISP, which is I believe what Javier was asking about, the
> >>> application will set the format on the OMAP3 ISP resizer input and output pads
> >>> to configure scaling.
> >>
> >
> > Yes, that was my question about. But still is not clear to me if
> > configuring the ISP resizer input and output pads with different frame
> > sizes automatically means that I have to do the scale or this has to
> > be configured using a S_FMT ioctl to the /dev/video? node.
> >
> > Basically what I don't know is when I have to modify the pipeline
> > graph inside the ISP driver and when this has to be made from
> > user-space via MCF.
>
> In the specific case of analog inputs, In general, better results are obtained
> if the scaling is done at the analog demod, as it can play with the pixel
> sampling rate, and obtaining a better result than a decimation filter. Not
> all demods accept this through.
>
> Anyway, S_FMT is expected to work at the /dev/video? node. Laurent will likely
> argument against, but, again, allowing to control the scaling on a different
> place is a bonus of the MC/subdev API, but it should never replace the S_FMT
> V4L2 call.
I agree with Mauro, up to a point. One way or another drivers should support S_FMT
through the video nodes. But if someone starts programming the pipeline through
subdev nodes, then I think it is reasonable that trying to call S_FMT would return
EBUSY or something similar.
It has been suggested that S_FMT can be implemented for such systems as a libv4l2
plugin, but I would like to see code doing this first as I am not convinced that
that's the best way to do it.
Regards,
Hans
> >> The V4L2 API doesn't tell where a function like scaler will be implemented.
> >> So, it is fine to implement it at tvp5151 or at the omap3 resizer, when a
> >> V4L2 call is sent.
> >>
> >
> > I don't think I can do the cropping and scaling in the tvp5151 driver
> > since this is a dumb device, it only spits bytes via its parallel
> > interface. The actual buffer is inside the ISP.
>
> I wrote the tvp5150 driver from scratch a long time ago. Can't remember all
> details anymore. As far as I can remember, I don't think it has scaling. Also,
> its sampler seems to use a fixed pixel clock rate.
>
> It does support crop by adjusting the blank registers. Probably there's a
> limit to the range that cropping can be done, but, in general, it should be enough
> to remove the black lines from the borders (and the teletext/cc info).
>
> I can't think on any advantage of doing cropping at tvp5150. So, you can just
> implement it where you're more comfortable with.
>
> Regards,
> Mauro
>
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