This patch serie allows to connect non-parallel camera sensor to
DCMI thanks to a bridge connected in between such as STMIPID02 [1].
Media controller support is introduced first, then support of
several sub-devices within pipeline with dynamic linking
between them.
In order to keep backward compatibility with applications
relying on V4L2 interface only, format set on video node
is propagated to all sub-devices connected to camera interface.
[1] https://www.spinics.net/lists/devicetree/msg278002.html
===========
= history =
===========
version 2:
- Fix bus_info not consistent between media and V4L:
https://www.spinics.net/lists/arm-kernel/msg717676.html
- Propagation of format set on video node to the sub-devices
chain connected on camera interface
version 1:
- Initial submission
Hugues Fruchet (3):
media: stm32-dcmi: improve sensor subdev naming
media: stm32-dcmi: add media controller support
media: stm32-dcmi: add support of several sub-devices
drivers/media/platform/Kconfig | 2 +-
drivers/media/platform/stm32/stm32-dcmi.c | 317 +++++++++++++++++++++++++-----
2 files changed, 266 insertions(+), 53 deletions(-)
--
2.7.4
Hi Hugues,
On Tue, Jun 11, 2019 at 10:48:29AM +0200, Hugues Fruchet wrote:
> This patch serie allows to connect non-parallel camera sensor to
> DCMI thanks to a bridge connected in between such as STMIPID02 [1].
>
> Media controller support is introduced first, then support of
> several sub-devices within pipeline with dynamic linking
> between them.
> In order to keep backward compatibility with applications
> relying on V4L2 interface only, format set on video node
> is propagated to all sub-devices connected to camera interface.
>
> [1] https://www.spinics.net/lists/devicetree/msg278002.html
General notes on the set, not related to any single patch:
- Where's the sub-device representing the bridge itself?
- As the driver becomes MC-centric, crop configuration takes place through
V4L2 sub-device interface, not through the video device node.
- Same goes for accessing sensor configuration: it does not take place
through video node but through the sub-device nodes.
--
Kind regards,
Sakari Ailus
[email protected]
Hi Sakari,
> - Where's the sub-device representing the bridge itself?
This is pointed by [1]: drivers/media/i2c/st-mipid02.c
> - As the driver becomes MC-centric, crop configuration takes place
through
> V4L2 sub-device interface, not through the video device node.
> - Same goes for accessing sensor configuration: it does not take place
> through video node but through the sub-device nodes.
Our objective is to be able to support either a simple parallel sensor
or a CSI-2 sensor connected through a bridge without any changes on
userspace side because no additional processing or conversion involved,
only deserialisation is m.
With the proposed set of patches, we succeeded to do so, the same
non-regression tests campaign is passed with OV5640 parallel sensor
(STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
D3 mezzanine board).
We don't want driver to be MC-centric, media controller support was
required only to get access to the set of functions needed to link and
walk trough subdevices: media_create_pad_link(),
media_entity_remote_pad(), etc...
We did a try with the v1 version of this patchset, delegating subdevices
handling to userspace, by using media-controller, but this require to
configure first the pipeline for each single change of resolution and
format before making any capture using v4l2-ctl or GStreamer, quite
heavy in fact.
Benjamin did another try using new libcamera codebase, but even for a
basic capture use-case, negotiation code is quite tricky in order to
match the right subdevices bus format to the required V4L2 format.
Moreover, it was not clear how to call libcamera library prior to any
v4l2-ctl or GStreamer calls.
Adding 100 lines of code into DCMI to well configure resolution and
formats fixes the point and allows us to keep backward compatibility
as per our objective, so it seems far more reasonable to us to do so
even if DCMI controls more than the subdevice it is connected to.
Moreover we found similar code in other video interfaces code like
qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
pipeline, so it seems to us quite natural to go this way.
To summarize, if we cannot do the negotiation within kernel, delegating
this to userspace implies far more complexity and breaks compatibility
with existing applications without adding new functionalities.
Having all that in mind, what should be reconsidered in your opinion
Sakari ? Do you have some alternatives ?
Best regards,
Hugues.
On 6/20/19 6:17 PM, Sakari Ailus wrote:
> Hi Hugues,
>
> On Tue, Jun 11, 2019 at 10:48:29AM +0200, Hugues Fruchet wrote:
>> This patch serie allows to connect non-parallel camera sensor to
>> DCMI thanks to a bridge connected in between such as STMIPID02 [1].
>>
>> Media controller support is introduced first, then support of
>> several sub-devices within pipeline with dynamic linking
>> between them.
>> In order to keep backward compatibility with applications
>> relying on V4L2 interface only, format set on video node
>> is propagated to all sub-devices connected to camera interface.
>>
>> [1] https://www.spinics.net/lists/devicetree/msg278002.html
>
> General notes on the set, not related to any single patch:
>
> - Where's the sub-device representing the bridge itself?
>
> - As the driver becomes MC-centric, crop configuration takes place through
> V4L2 sub-device interface, not through the video device node.
>
> - Same goes for accessing sensor configuration: it does not take place
> through video node but through the sub-device nodes.
>
Hi Hugues,
On Mon, Jun 24, 2019 at 10:10:05AM +0000, Hugues FRUCHET wrote:
> Hi Sakari,
>
> > - Where's the sub-device representing the bridge itself?
> This is pointed by [1]: drivers/media/i2c/st-mipid02.c
>
> > - As the driver becomes MC-centric, crop configuration takes place
> through
> > V4L2 sub-device interface, not through the video device node.
> > - Same goes for accessing sensor configuration: it does not take place
> > through video node but through the sub-device nodes.
>
> Our objective is to be able to support either a simple parallel sensor
> or a CSI-2 sensor connected through a bridge without any changes on
> userspace side because no additional processing or conversion involved,
> only deserialisation is m.
> With the proposed set of patches, we succeeded to do so, the same
> non-regression tests campaign is passed with OV5640 parallel sensor
> (STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
> D3 mezzanine board).
>
> We don't want driver to be MC-centric, media controller support was
> required only to get access to the set of functions needed to link and
> walk trough subdevices: media_create_pad_link(),
> media_entity_remote_pad(), etc...
>
> We did a try with the v1 version of this patchset, delegating subdevices
> handling to userspace, by using media-controller, but this require to
> configure first the pipeline for each single change of resolution and
> format before making any capture using v4l2-ctl or GStreamer, quite
> heavy in fact.
> Benjamin did another try using new libcamera codebase, but even for a
> basic capture use-case, negotiation code is quite tricky in order to
> match the right subdevices bus format to the required V4L2 format.
Why would it be trickier in userspace than in the kernel ? The V4L2
subdev operations are more or less expose verbatim through the subdev
userspace API.
> Moreover, it was not clear how to call libcamera library prior to any
> v4l2-ctl or GStreamer calls.
libcamera isn't meant to be called before v4l2-ctl or GStreamer.
Applications are supposed to be based directly on libcamera, or, for
existing userspace APIs such as V4L2 or GStreamer, compatibility layers
are supposed to be developed. For V4L2 it will take the form of a
LD_PRELOAD-able .so that will intercept the V4L2 API calls, making most
V4L2 applications work with libcamera unmodified (I said most as 100%
compatibility will likely not be achievable). For GStreamer it will take
the form of a GStreamer libcamera element that will replace the V4L2
source element.
> Adding 100 lines of code into DCMI to well configure resolution and
> formats fixes the point and allows us to keep backward compatibility
> as per our objective, so it seems far more reasonable to us to do so
> even if DCMI controls more than the subdevice it is connected to.
> Moreover we found similar code in other video interfaces code like
> qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
> pipeline, so it seems to us quite natural to go this way.
I can't comment on the qcom-camss driver as I'm not aware of its
internals, but where have you found such code in the Xilinx V4L2 drivers
?
> To summarize, if we cannot do the negotiation within kernel, delegating
> this to userspace implies far more complexity and breaks compatibility
> with existing applications without adding new functionalities.
>
> Having all that in mind, what should be reconsidered in your opinion
> Sakari ? Do you have some alternatives ?
First of all, let's note that your patch series performs to related but
still independent changes: it enables MC support, *and* enables the V4L2
subdev userspace API. The former is clearly needed and will allow you to
use the MC API internally in the kernel, simplifying pipeline traversal.
The latter then enables the V4L2 subdev userspace API, moving the
pipeline configuration responsibility to userspace.
You could in theory move to the MC API inside the kernel, without
enabling support for the V4L2 subdev userspace API. Configuring the
pipeline and propagating the formats would then be the responsibility of
the kernel driver. However, this will limit your driver to the
following:
- Fully linear pipelines only (single sensor)
- No support for controls implemented by multiple entities in the
pipeline (for instance controls that would exist in both the sensor
and the bridge, such as gains)
- No proper support for scaling configuration if multiple components in
the pipeline can scale
Are you willing to set those limitations in stone and give up on
supporting those features ?
> On 6/20/19 6:17 PM, Sakari Ailus wrote:
> > On Tue, Jun 11, 2019 at 10:48:29AM +0200, Hugues Fruchet wrote:
> >> This patch serie allows to connect non-parallel camera sensor to
> >> DCMI thanks to a bridge connected in between such as STMIPID02 [1].
> >>
> >> Media controller support is introduced first, then support of
> >> several sub-devices within pipeline with dynamic linking
> >> between them.
> >> In order to keep backward compatibility with applications
> >> relying on V4L2 interface only, format set on video node
> >> is propagated to all sub-devices connected to camera interface.
> >>
> >> [1] https://www.spinics.net/lists/devicetree/msg278002.html
> >
> > General notes on the set, not related to any single patch:
> >
> > - Where's the sub-device representing the bridge itself?
> >
> > - As the driver becomes MC-centric, crop configuration takes place through
> > V4L2 sub-device interface, not through the video device node.
> >
> > - Same goes for accessing sensor configuration: it does not take place
> > through video node but through the sub-device nodes.
> >
--
Regards,
Laurent Pinchart
Hi Laurent,
Thanks for reviewing,
On 6/26/19 7:25 PM, Laurent Pinchart wrote:
> Hi Hugues,
>
> On Mon, Jun 24, 2019 at 10:10:05AM +0000, Hugues FRUCHET wrote:
>> Hi Sakari,
>>
>> > - Where's the sub-device representing the bridge itself?
>> This is pointed by [1]: drivers/media/i2c/st-mipid02.c
>>
>> > - As the driver becomes MC-centric, crop configuration takes place
>> through
>> > V4L2 sub-device interface, not through the video device node.
>> > - Same goes for accessing sensor configuration: it does not take place
>> > through video node but through the sub-device nodes.
>>
>> Our objective is to be able to support either a simple parallel sensor
>> or a CSI-2 sensor connected through a bridge without any changes on
>> userspace side because no additional processing or conversion involved,
>> only deserialisation is m.
>> With the proposed set of patches, we succeeded to do so, the same
>> non-regression tests campaign is passed with OV5640 parallel sensor
>> (STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
>> D3 mezzanine board).
>>
>> We don't want driver to be MC-centric, media controller support was
>> required only to get access to the set of functions needed to link and
>> walk trough subdevices: media_create_pad_link(),
>> media_entity_remote_pad(), etc...
>>
>> We did a try with the v1 version of this patchset, delegating subdevices
>> handling to userspace, by using media-controller, but this require to
>> configure first the pipeline for each single change of resolution and
>> format before making any capture using v4l2-ctl or GStreamer, quite
>> heavy in fact.
>> Benjamin did another try using new libcamera codebase, but even for a
>> basic capture use-case, negotiation code is quite tricky in order to
>> match the right subdevices bus format to the required V4L2 format.
>
> Why would it be trickier in userspace than in the kernel ? The V4L2
> subdev operations are more or less expose verbatim through the subdev
> userspace API.
>
>> Moreover, it was not clear how to call libcamera library prior to any
>> v4l2-ctl or GStreamer calls.
>
> libcamera isn't meant to be called before v4l2-ctl or GStreamer.
> Applications are supposed to be based directly on libcamera, or, for
> existing userspace APIs such as V4L2 or GStreamer, compatibility layers
> are supposed to be developed. For V4L2 it will take the form of a
> LD_PRELOAD-able .so that will intercept the V4L2 API calls, making most
> V4L2 applications work with libcamera unmodified (I said most as 100%
> compatibility will likely not be achievable). For GStreamer it will take
> the form of a GStreamer libcamera element that will replace the V4L2
> source element.
>
>> Adding 100 lines of code into DCMI to well configure resolution and
>> formats fixes the point and allows us to keep backward compatibility
>> as per our objective, so it seems far more reasonable to us to do so
>> even if DCMI controls more than the subdevice it is connected to.
>> Moreover we found similar code in other video interfaces code like
>> qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
>> pipeline, so it seems to us quite natural to go this way.
>
> I can't comment on the qcom-camss driver as I'm not aware of its
> internals, but where have you found such code in the Xilinx V4L2 drivers
> ?
For ex. in xilinx/xilinx-dma.c, stream on/off is propagated to all
subdevices within pipeline:
* Walk the entities chain starting at the pipeline output video node
static int xvip_pipeline_start_stop(struct xvip_pipeline *pipe, bool start)
Same for qcom/camss/camss-video.c:
static int video_start_streaming(struct vb2_queue *q, unsigned int count)
For resolution/format, in exynos4-is/fimc-capture.c:
static int fimc_pipeline_try_format(struct fimc_ctx *ctx,
...
while (1) {
...
/* set format on all pipeline subdevs */
while (me != &fimc->vid_cap.subdev.entity) {
...
ret = v4l2_subdev_call(sd, pad, set_fmt, NULL, &sfmt);
>
>> To summarize, if we cannot do the negotiation within kernel, delegating
>> this to userspace implies far more complexity and breaks compatibility
>> with existing applications without adding new functionalities.
>>
>> Having all that in mind, what should be reconsidered in your opinion
>> Sakari ? Do you have some alternatives ?
>
> First of all, let's note that your patch series performs to related but
> still independent changes: it enables MC support, *and* enables the V4L2
> subdev userspace API. The former is clearly needed and will allow you to
> use the MC API internally in the kernel, simplifying pipeline traversal.
> The latter then enables the V4L2 subdev userspace API, moving the
> pipeline configuration responsibility to userspace.
>
> You could in theory move to the MC API inside the kernel, without
> enabling support for the V4L2 subdev userspace API. Configuring the
> pipeline and propagating the formats would then be the responsibility of
> the kernel driver.
Yes this is exactly what we want to do.
If I understand well, to disable the V4L2 subdev userspace API, I just
have to remove the media device registry:
- /* Register the media device */
- ret = media_device_register(&dcmi->mdev);
- if (ret) {
- dev_err(dcmi->dev, "Failed to register media device (%d)\n",
- ret);
- goto err_media_device_cleanup;
- }
Do you see any additional things to do ?
> However, this will limit your driver to the
> following:
>
> - Fully linear pipelines only (single sensor)
> - No support for controls implemented by multiple entities in the
> pipeline (for instance controls that would exist in both the sensor
> and the bridge, such as gains)
> - No proper support for scaling configuration if multiple components in
> the pipeline can scale
>
> Are you willing to set those limitations in stone and give up on
> supporting those features ?
>
The involved hardware do not have those features, no need of extra
functionalities to be exposed to userspace, so this is fine.
I'll push a v3 with this change and the other fixes related to Sakari
and Hans comments.
Please Sakari & Hans, also comment on that change that we can converge
on v3.
Best regards,
Hugues.
Hi Hugues,
On Thu, Jun 27, 2019 at 12:38:40PM +0000, Hugues FRUCHET wrote:
> On 6/26/19 7:25 PM, Laurent Pinchart wrote:
> > On Mon, Jun 24, 2019 at 10:10:05AM +0000, Hugues FRUCHET wrote:
> >> Hi Sakari,
> >>
> >>> - Where's the sub-device representing the bridge itself?
> >>
> >> This is pointed by [1]: drivers/media/i2c/st-mipid02.c
> >>
> >>> - As the driver becomes MC-centric, crop configuration takes place through
> >>> V4L2 sub-device interface, not through the video device node.
> >>> - Same goes for accessing sensor configuration: it does not take place
> >>> through video node but through the sub-device nodes.
> >>
> >> Our objective is to be able to support either a simple parallel sensor
> >> or a CSI-2 sensor connected through a bridge without any changes on
> >> userspace side because no additional processing or conversion involved,
> >> only deserialisation is m.
> >> With the proposed set of patches, we succeeded to do so, the same
> >> non-regression tests campaign is passed with OV5640 parallel sensor
> >> (STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
> >> D3 mezzanine board).
> >>
> >> We don't want driver to be MC-centric, media controller support was
> >> required only to get access to the set of functions needed to link and
> >> walk trough subdevices: media_create_pad_link(),
> >> media_entity_remote_pad(), etc...
> >>
> >> We did a try with the v1 version of this patchset, delegating subdevices
> >> handling to userspace, by using media-controller, but this require to
> >> configure first the pipeline for each single change of resolution and
> >> format before making any capture using v4l2-ctl or GStreamer, quite
> >> heavy in fact.
> >> Benjamin did another try using new libcamera codebase, but even for a
> >> basic capture use-case, negotiation code is quite tricky in order to
> >> match the right subdevices bus format to the required V4L2 format.
> >
> > Why would it be trickier in userspace than in the kernel ? The V4L2
> > subdev operations are more or less expose verbatim through the subdev
> > userspace API.
> >
> >> Moreover, it was not clear how to call libcamera library prior to any
> >> v4l2-ctl or GStreamer calls.
> >
> > libcamera isn't meant to be called before v4l2-ctl or GStreamer.
> > Applications are supposed to be based directly on libcamera, or, for
> > existing userspace APIs such as V4L2 or GStreamer, compatibility layers
> > are supposed to be developed. For V4L2 it will take the form of a
> > LD_PRELOAD-able .so that will intercept the V4L2 API calls, making most
> > V4L2 applications work with libcamera unmodified (I said most as 100%
> > compatibility will likely not be achievable). For GStreamer it will take
> > the form of a GStreamer libcamera element that will replace the V4L2
> > source element.
> >
> >> Adding 100 lines of code into DCMI to well configure resolution and
> >> formats fixes the point and allows us to keep backward compatibility
> >> as per our objective, so it seems far more reasonable to us to do so
> >> even if DCMI controls more than the subdevice it is connected to.
> >> Moreover we found similar code in other video interfaces code like
> >> qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
> >> pipeline, so it seems to us quite natural to go this way.
> >
> > I can't comment on the qcom-camss driver as I'm not aware of its
> > internals, but where have you found such code in the Xilinx V4L2 drivers
> > ?
>
> For ex. in xilinx/xilinx-dma.c, stream on/off is propagated to all
> subdevices within pipeline:
> * Walk the entities chain starting at the pipeline output video node
> static int xvip_pipeline_start_stop(struct xvip_pipeline *pipe, bool start)
>
> Same for qcom/camss/camss-video.c:
> static int video_start_streaming(struct vb2_queue *q, unsigned int count)
For stream start/stop, that's expected. Userspace only controls the
stream start/stop on the video node, and the kernel propagates that
along the pipeline. There is no VIDIOC_STREAMON or VIDIOC_STREAMOFF
ioctl exposed to userspace for V4L2 subdevs. What is not propagated in
the kernel for MC-centric devices is the pipeline configuration (formats
and selection rectangles).
> For resolution/format, in exynos4-is/fimc-capture.c:
> static int fimc_pipeline_try_format(struct fimc_ctx *ctx,
> ...
> while (1) {
> ...
> /* set format on all pipeline subdevs */
> while (me != &fimc->vid_cap.subdev.entity) {
> ...
> ret = v4l2_subdev_call(sd, pad, set_fmt, NULL, &sfmt);
As explained below, propagating formats is fine for video node-centric
drivers, but comes with limitations.
> >> To summarize, if we cannot do the negotiation within kernel, delegating
> >> this to userspace implies far more complexity and breaks compatibility
> >> with existing applications without adding new functionalities.
> >>
> >> Having all that in mind, what should be reconsidered in your opinion
> >> Sakari ? Do you have some alternatives ?
> >
> > First of all, let's note that your patch series performs to related but
> > still independent changes: it enables MC support, *and* enables the V4L2
> > subdev userspace API. The former is clearly needed and will allow you to
> > use the MC API internally in the kernel, simplifying pipeline traversal.
> > The latter then enables the V4L2 subdev userspace API, moving the
> > pipeline configuration responsibility to userspace.
> >
> > You could in theory move to the MC API inside the kernel, without
> > enabling support for the V4L2 subdev userspace API. Configuring the
> > pipeline and propagating the formats would then be the responsibility of
> > the kernel driver.
>
> Yes this is exactly what we want to do.
> If I understand well, to disable the V4L2 subdev userspace API, I just
> have to remove the media device registry:
>
> - /* Register the media device */
> - ret = media_device_register(&dcmi->mdev);
> - if (ret) {
> - dev_err(dcmi->dev, "Failed to register media device (%d)\n",
> - ret);
> - goto err_media_device_cleanup;
> - }
>
> Do you see any additional things to do ?
That should be it. Note that in that case pipeline configuration has to
be handled by the master driver (DCMI in this case), the external
subdevs involved (such as the CSI-2 to parallel bridge) must not handle
any propagation of formats or selection rectangles.
> > However, this will limit your driver to the
> > following:
> >
> > - Fully linear pipelines only (single sensor)
> > - No support for controls implemented by multiple entities in the
> > pipeline (for instance controls that would exist in both the sensor
> > and the bridge, such as gains)
> > - No proper support for scaling configuration if multiple components in
> > the pipeline can scale
> >
> > Are you willing to set those limitations in stone and give up on
> > supporting those features ?
> >
>
> The involved hardware do not have those features, no need of extra
> functionalities to be exposed to userspace, so this is fine.
>
> I'll push a v3 with this change and the other fixes related to Sakari
> and Hans comments.
>
> Please Sakari & Hans, also comment on that change that we can converge
> on v3.
--
Regards,
Laurent Pinchart
Hi Laurent,
On Thu, Jun 27, 2019 at 04:38:24PM +0300, Laurent Pinchart wrote:
> Hi Hugues,
>
> On Thu, Jun 27, 2019 at 12:38:40PM +0000, Hugues FRUCHET wrote:
> > On 6/26/19 7:25 PM, Laurent Pinchart wrote:
> > > On Mon, Jun 24, 2019 at 10:10:05AM +0000, Hugues FRUCHET wrote:
> > >> Hi Sakari,
> > >>
> > >>> - Where's the sub-device representing the bridge itself?
> > >>
> > >> This is pointed by [1]: drivers/media/i2c/st-mipid02.c
> > >>
> > >>> - As the driver becomes MC-centric, crop configuration takes place through
> > >>> V4L2 sub-device interface, not through the video device node.
> > >>> - Same goes for accessing sensor configuration: it does not take place
> > >>> through video node but through the sub-device nodes.
> > >>
> > >> Our objective is to be able to support either a simple parallel sensor
> > >> or a CSI-2 sensor connected through a bridge without any changes on
> > >> userspace side because no additional processing or conversion involved,
> > >> only deserialisation is m.
> > >> With the proposed set of patches, we succeeded to do so, the same
> > >> non-regression tests campaign is passed with OV5640 parallel sensor
> > >> (STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
> > >> D3 mezzanine board).
> > >>
> > >> We don't want driver to be MC-centric, media controller support was
> > >> required only to get access to the set of functions needed to link and
> > >> walk trough subdevices: media_create_pad_link(),
> > >> media_entity_remote_pad(), etc...
> > >>
> > >> We did a try with the v1 version of this patchset, delegating subdevices
> > >> handling to userspace, by using media-controller, but this require to
> > >> configure first the pipeline for each single change of resolution and
> > >> format before making any capture using v4l2-ctl or GStreamer, quite
> > >> heavy in fact.
> > >> Benjamin did another try using new libcamera codebase, but even for a
> > >> basic capture use-case, negotiation code is quite tricky in order to
> > >> match the right subdevices bus format to the required V4L2 format.
> > >
> > > Why would it be trickier in userspace than in the kernel ? The V4L2
> > > subdev operations are more or less expose verbatim through the subdev
> > > userspace API.
> > >
> > >> Moreover, it was not clear how to call libcamera library prior to any
> > >> v4l2-ctl or GStreamer calls.
> > >
> > > libcamera isn't meant to be called before v4l2-ctl or GStreamer.
> > > Applications are supposed to be based directly on libcamera, or, for
> > > existing userspace APIs such as V4L2 or GStreamer, compatibility layers
> > > are supposed to be developed. For V4L2 it will take the form of a
> > > LD_PRELOAD-able .so that will intercept the V4L2 API calls, making most
> > > V4L2 applications work with libcamera unmodified (I said most as 100%
> > > compatibility will likely not be achievable). For GStreamer it will take
> > > the form of a GStreamer libcamera element that will replace the V4L2
> > > source element.
> > >
> > >> Adding 100 lines of code into DCMI to well configure resolution and
> > >> formats fixes the point and allows us to keep backward compatibility
> > >> as per our objective, so it seems far more reasonable to us to do so
> > >> even if DCMI controls more than the subdevice it is connected to.
> > >> Moreover we found similar code in other video interfaces code like
> > >> qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
> > >> pipeline, so it seems to us quite natural to go this way.
> > >
> > > I can't comment on the qcom-camss driver as I'm not aware of its
> > > internals, but where have you found such code in the Xilinx V4L2 drivers
> > > ?
> >
> > For ex. in xilinx/xilinx-dma.c, stream on/off is propagated to all
> > subdevices within pipeline:
> > * Walk the entities chain starting at the pipeline output video node
> > static int xvip_pipeline_start_stop(struct xvip_pipeline *pipe, bool start)
> >
> > Same for qcom/camss/camss-video.c:
> > static int video_start_streaming(struct vb2_queue *q, unsigned int count)
>
> For stream start/stop, that's expected. Userspace only controls the
> stream start/stop on the video node, and the kernel propagates that
> along the pipeline. There is no VIDIOC_STREAMON or VIDIOC_STREAMOFF
> ioctl exposed to userspace for V4L2 subdevs. What is not propagated in
> the kernel for MC-centric devices is the pipeline configuration (formats
> and selection rectangles).
>
> > For resolution/format, in exynos4-is/fimc-capture.c:
> > static int fimc_pipeline_try_format(struct fimc_ctx *ctx,
> > ...
> > while (1) {
> > ...
> > /* set format on all pipeline subdevs */
> > while (me != &fimc->vid_cap.subdev.entity) {
> > ...
> > ret = v4l2_subdev_call(sd, pad, set_fmt, NULL, &sfmt);
>
> As explained below, propagating formats is fine for video node-centric
> drivers, but comes with limitations.
>
> > >> To summarize, if we cannot do the negotiation within kernel, delegating
> > >> this to userspace implies far more complexity and breaks compatibility
> > >> with existing applications without adding new functionalities.
> > >>
> > >> Having all that in mind, what should be reconsidered in your opinion
> > >> Sakari ? Do you have some alternatives ?
> > >
> > > First of all, let's note that your patch series performs to related but
> > > still independent changes: it enables MC support, *and* enables the V4L2
> > > subdev userspace API. The former is clearly needed and will allow you to
> > > use the MC API internally in the kernel, simplifying pipeline traversal.
> > > The latter then enables the V4L2 subdev userspace API, moving the
> > > pipeline configuration responsibility to userspace.
> > >
> > > You could in theory move to the MC API inside the kernel, without
> > > enabling support for the V4L2 subdev userspace API. Configuring the
> > > pipeline and propagating the formats would then be the responsibility of
> > > the kernel driver.
> >
> > Yes this is exactly what we want to do.
> > If I understand well, to disable the V4L2 subdev userspace API, I just
> > have to remove the media device registry:
> >
> > - /* Register the media device */
> > - ret = media_device_register(&dcmi->mdev);
> > - if (ret) {
> > - dev_err(dcmi->dev, "Failed to register media device (%d)\n",
> > - ret);
> > - goto err_media_device_cleanup;
> > - }
> >
> > Do you see any additional things to do ?
>
> That should be it. Note that in that case pipeline configuration has to
> be handled by the master driver (DCMI in this case), the external
> subdevs involved (such as the CSI-2 to parallel bridge) must not handle
> any propagation of formats or selection rectangles.
I wonder what we'd do in the case when someone needs to connect something
else to the pipeline, such as a sensor with more than one sub-device, or a
flash or a lens controller.
For future-proofness, I'd just use MC for hardware that may be part of a
complex pipeline. In this case, if you think backwards compatibility is
important (and for most hardware it probably is), I don't think there are
perfect solutions if your existing driver is not MC-enabled.
A reasonable compromise would be to add a Kconfig option that allows
enabling MC. This way you can provide backwards compatibility and allow
making use of the full potential of the hardware. That's also why hardware
that may be part of a non-trivial MC pipeline should start with MC-enabled
so we wouldn't run into this.
--
Kind regards,
Sakari Ailus
[email protected]
Hi Sakari,
On Fri, Jul 05, 2019 at 10:55:22AM +0300, Sakari Ailus wrote:
> On Thu, Jun 27, 2019 at 04:38:24PM +0300, Laurent Pinchart wrote:
> > On Thu, Jun 27, 2019 at 12:38:40PM +0000, Hugues FRUCHET wrote:
> >> On 6/26/19 7:25 PM, Laurent Pinchart wrote:
> >>> On Mon, Jun 24, 2019 at 10:10:05AM +0000, Hugues FRUCHET wrote:
> >>>> Hi Sakari,
> >>>>
> >>>>> - Where's the sub-device representing the bridge itself?
> >>>>
> >>>> This is pointed by [1]: drivers/media/i2c/st-mipid02.c
> >>>>
> >>>>> - As the driver becomes MC-centric, crop configuration takes place through
> >>>>> V4L2 sub-device interface, not through the video device node.
> >>>>> - Same goes for accessing sensor configuration: it does not take place
> >>>>> through video node but through the sub-device nodes.
> >>>>
> >>>> Our objective is to be able to support either a simple parallel sensor
> >>>> or a CSI-2 sensor connected through a bridge without any changes on
> >>>> userspace side because no additional processing or conversion involved,
> >>>> only deserialisation is m.
> >>>> With the proposed set of patches, we succeeded to do so, the same
> >>>> non-regression tests campaign is passed with OV5640 parallel sensor
> >>>> (STM32MP1 evaluation board) or OV5640 CSI-2 sensor (Avenger96 board with
> >>>> D3 mezzanine board).
> >>>>
> >>>> We don't want driver to be MC-centric, media controller support was
> >>>> required only to get access to the set of functions needed to link and
> >>>> walk trough subdevices: media_create_pad_link(),
> >>>> media_entity_remote_pad(), etc...
> >>>>
> >>>> We did a try with the v1 version of this patchset, delegating subdevices
> >>>> handling to userspace, by using media-controller, but this require to
> >>>> configure first the pipeline for each single change of resolution and
> >>>> format before making any capture using v4l2-ctl or GStreamer, quite
> >>>> heavy in fact.
> >>>> Benjamin did another try using new libcamera codebase, but even for a
> >>>> basic capture use-case, negotiation code is quite tricky in order to
> >>>> match the right subdevices bus format to the required V4L2 format.
> >>>
> >>> Why would it be trickier in userspace than in the kernel ? The V4L2
> >>> subdev operations are more or less expose verbatim through the subdev
> >>> userspace API.
> >>>
> >>>> Moreover, it was not clear how to call libcamera library prior to any
> >>>> v4l2-ctl or GStreamer calls.
> >>>
> >>> libcamera isn't meant to be called before v4l2-ctl or GStreamer.
> >>> Applications are supposed to be based directly on libcamera, or, for
> >>> existing userspace APIs such as V4L2 or GStreamer, compatibility layers
> >>> are supposed to be developed. For V4L2 it will take the form of a
> >>> LD_PRELOAD-able .so that will intercept the V4L2 API calls, making most
> >>> V4L2 applications work with libcamera unmodified (I said most as 100%
> >>> compatibility will likely not be achievable). For GStreamer it will take
> >>> the form of a GStreamer libcamera element that will replace the V4L2
> >>> source element.
> >>>
> >>>> Adding 100 lines of code into DCMI to well configure resolution and
> >>>> formats fixes the point and allows us to keep backward compatibility
> >>>> as per our objective, so it seems far more reasonable to us to do so
> >>>> even if DCMI controls more than the subdevice it is connected to.
> >>>> Moreover we found similar code in other video interfaces code like
> >>>> qcom/camss/camss.c and xilinx/xilinx-dma.c, controlling the whole
> >>>> pipeline, so it seems to us quite natural to go this way.
> >>>
> >>> I can't comment on the qcom-camss driver as I'm not aware of its
> >>> internals, but where have you found such code in the Xilinx V4L2 drivers
> >>> ?
> >>
> >> For ex. in xilinx/xilinx-dma.c, stream on/off is propagated to all
> >> subdevices within pipeline:
> >> * Walk the entities chain starting at the pipeline output video node
> >> static int xvip_pipeline_start_stop(struct xvip_pipeline *pipe, bool start)
> >>
> >> Same for qcom/camss/camss-video.c:
> >> static int video_start_streaming(struct vb2_queue *q, unsigned int count)
> >
> > For stream start/stop, that's expected. Userspace only controls the
> > stream start/stop on the video node, and the kernel propagates that
> > along the pipeline. There is no VIDIOC_STREAMON or VIDIOC_STREAMOFF
> > ioctl exposed to userspace for V4L2 subdevs. What is not propagated in
> > the kernel for MC-centric devices is the pipeline configuration (formats
> > and selection rectangles).
> >
> >> For resolution/format, in exynos4-is/fimc-capture.c:
> >> static int fimc_pipeline_try_format(struct fimc_ctx *ctx,
> >> ...
> >> while (1) {
> >> ...
> >> /* set format on all pipeline subdevs */
> >> while (me != &fimc->vid_cap.subdev.entity) {
> >> ...
> >> ret = v4l2_subdev_call(sd, pad, set_fmt, NULL, &sfmt);
> >
> > As explained below, propagating formats is fine for video node-centric
> > drivers, but comes with limitations.
> >
> >>>> To summarize, if we cannot do the negotiation within kernel, delegating
> >>>> this to userspace implies far more complexity and breaks compatibility
> >>>> with existing applications without adding new functionalities.
> >>>>
> >>>> Having all that in mind, what should be reconsidered in your opinion
> >>>> Sakari ? Do you have some alternatives ?
> >>>
> >>> First of all, let's note that your patch series performs to related but
> >>> still independent changes: it enables MC support, *and* enables the V4L2
> >>> subdev userspace API. The former is clearly needed and will allow you to
> >>> use the MC API internally in the kernel, simplifying pipeline traversal.
> >>> The latter then enables the V4L2 subdev userspace API, moving the
> >>> pipeline configuration responsibility to userspace.
> >>>
> >>> You could in theory move to the MC API inside the kernel, without
> >>> enabling support for the V4L2 subdev userspace API. Configuring the
> >>> pipeline and propagating the formats would then be the responsibility of
> >>> the kernel driver.
> >>
> >> Yes this is exactly what we want to do.
> >> If I understand well, to disable the V4L2 subdev userspace API, I just
> >> have to remove the media device registry:
> >>
> >> - /* Register the media device */
> >> - ret = media_device_register(&dcmi->mdev);
> >> - if (ret) {
> >> - dev_err(dcmi->dev, "Failed to register media device (%d)\n",
> >> - ret);
> >> - goto err_media_device_cleanup;
> >> - }
> >>
> >> Do you see any additional things to do ?
> >
> > That should be it. Note that in that case pipeline configuration has to
> > be handled by the master driver (DCMI in this case), the external
> > subdevs involved (such as the CSI-2 to parallel bridge) must not handle
> > any propagation of formats or selection rectangles.
>
> I wonder what we'd do in the case when someone needs to connect something
> else to the pipeline, such as a sensor with more than one sub-device, or a
> flash or a lens controller.
>
> For future-proofness, I'd just use MC for hardware that may be part of a
> complex pipeline. In this case, if you think backwards compatibility is
> important (and for most hardware it probably is), I don't think there are
> perfect solutions if your existing driver is not MC-enabled.
Oh, I fully agree with you, which is why I mentioned in another e-mail
that using a video node-centric approach would come with limitations,
such as not being able to support more complex pipelines, ever.
> A reasonable compromise would be to add a Kconfig option that allows
> enabling MC. This way you can provide backwards compatibility and allow
> making use of the full potential of the hardware. That's also why hardware
> that may be part of a non-trivial MC pipeline should start with MC-enabled
> so we wouldn't run into this.
I really don't like this, as it introduces additional complexity. My
recommendation is to go for an MC-centric approach. Going for a video
node-centric approach is really shooting oneself in the foot regarding
future extensions. But that being said, if there's a strong desire to go
for foot self-shooting, the way to go is explained above.
--
Regards,
Laurent Pinchart
Hi Laurent,
On Fri, Jul 05, 2019 at 11:04:24AM +0300, Laurent Pinchart wrote:
...
> > A reasonable compromise would be to add a Kconfig option that allows
> > enabling MC. This way you can provide backwards compatibility and allow
> > making use of the full potential of the hardware. That's also why hardware
> > that may be part of a non-trivial MC pipeline should start with MC-enabled
> > so we wouldn't run into this.
>
> I really don't like this, as it introduces additional complexity. My
> recommendation is to go for an MC-centric approach. Going for a video
> node-centric approach is really shooting oneself in the foot regarding
> future extensions. But that being said, if there's a strong desire to go
> for foot self-shooting, the way to go is explained above.
Well, there's nothing that can be done anymore as this has already
happened: this is an existing driver in the mainline kernel. Unless you
have a time machine of some sort, of course. :-) The choice is now really
between breaking existing applications (plain V4L2) and supporting new
functionality (MC-centric), so if you need both, I don't really see another
choice than a Kconfig option.
On the other hand, if we know there are no existing users that could not
support the MC-centric view of the device, we could just change the driver
API and forget the Kconfig option. It'd be much more simple that way
indeed. But I don'k know what's the case.
--
Regards,
Sakari Ailus
[email protected]