V4L2 device node centric - Was: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
Em Mon, 28 Aug 2017 11:41:58 +0200 Hans Verkuil escreveu: > > +control, and thus can't be used by **v4l2-centric** applications. > > vdev-centric > > TBD: I still think I prefer V4L2-centric over vdev-centric. I'm splitting it on a separate thread, to make easier for us to discuss. For those that aren't tracking the patchset that are documenting those terms, when MC was added, we got a hole new series of V4L2 devices that are incompatible with standard V4L2 applications, as they require knowledge about the hardware sub-devices. We are referring to such devices as MC-centric. We need another term to refer to the V4L2 devices that can be used by a generic application, and are fully controlled via a V4L2 device (/dev/video*, /dev/radio*, /dev/swradio*, /dev/vbi*, /dev/v4l-touch*). The proposed documentation patch series solves this issue by adding a glossary (patch 1) that defines what a "V4L2 device node" as: V4L2 device node A device node that it is associated to a V4L2 main driver, as specified at :ref:`v4l2_device_naming`. And, at the device naming chapter, at the spec (patch 2), it explicitly lists all V4L2 device node names: .. _v4l2_device_naming: V4L2 Device Node Naming === ... The existing V4L2 device node types are: == Default device node name Usage == ``/dev/videoX`` Video input/output devices ``/dev/vbiX``Vertical blank data (i.e. closed captions, teletext) ``/dev/radioX`` Radio tuners and modulators ``/dev/swradioX``Software Defined Radio tuners and modulators ``/dev/v4l-touchX`` Touch sensors == So, the concept of "V4L2 Device Node" is now clear, and doesn't include V4L2 sub-device device nodes (/dev/v4l-subdev*). For devices controlled via media controller, everybody seems to be comfortable of calling them as MC-centric. There are currently two proposals to refer to the media hardware that is controlled via a V4L2 Device Node: - vdev-centric - V4L2-centric The last one sounds confusing to me, as subdev API is part of the V4L2 specification. "V4L2-centric" name sounds to include subdevs. That's why IMHO, vdev-centric is better. We could go to some other naming for them, that would also be an alias for "V4L2 Device Node": - VD-centric - VDN-centric Comments? Thanks, Mauro
Re: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
On 26/08/17 13:53, Mauro Carvalho Chehab wrote:
> As both vdev-centric and MC-centric devices may implement the
> same APIs, we need a flag to allow userspace to distinguish
> between them.
>
> Signed-off-by: Mauro Carvalho Chehab
> ---
> Documentation/media/uapi/v4l/open.rst| 7 +++
> Documentation/media/uapi/v4l/vidioc-querycap.rst | 5 +
> Documentation/media/videodev2.h.rst.exceptions | 1 +
> include/uapi/linux/videodev2.h | 2 ++
> 4 files changed, 15 insertions(+)
>
> diff --git a/Documentation/media/uapi/v4l/open.rst
> b/Documentation/media/uapi/v4l/open.rst
> index 64b1de047b1b..d0930fc170f0 100644
> --- a/Documentation/media/uapi/v4l/open.rst
> +++ b/Documentation/media/uapi/v4l/open.rst
> @@ -46,6 +46,13 @@ the periferal can be used. For such devices, the
> sub-devices' configuration
> can be controlled via the :ref:`sub-device API `, which creates one
> device node per sub-device.
>
> +.. attention::
> +
> + Devices that require **mc-centric** hardware peripheral control should
MC-centric
As mentioned in my review of a previous patch I dislike the term "peripheral".
I think it should be dropped here.
> + report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
> + (see :ref:`VIDIOC_QUERYCAP`).
> +
> +
> In summary, for **MC-centric** hardware peripheral control:
>
> - The **V4L2 device** node is responsible for controlling the streaming
> diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst
> b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> index 12e0d9a63cd8..2b08723375bc 100644
> --- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
> +++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
> @@ -252,6 +252,11 @@ specification the ioctl returns an ``EINVAL`` error code.
> * - ``V4L2_CAP_TOUCH``
>- 0x1000
>- This is a touch device.
> +* - ``V4L2_MC_CENTRIC``
> + - 0x2000
> + - Indicates that the device require **mc-centric** hardware
MC-centric
> +control, and thus can't be used by **v4l2-centric** applications.
vdev-centric
TBD: I still think I prefer V4L2-centric over vdev-centric.
> +See :ref:`v4l2_hardware_control` for more details.
> * - ``V4L2_CAP_DEVICE_CAPS``
>- 0x8000
>- The driver fills the ``device_caps`` field. This capability can
> diff --git a/Documentation/media/videodev2.h.rst.exceptions
> b/Documentation/media/videodev2.h.rst.exceptions
> index a5cb0a8686ac..b51a575f9f75 100644
> --- a/Documentation/media/videodev2.h.rst.exceptions
> +++ b/Documentation/media/videodev2.h.rst.exceptions
> @@ -157,6 +157,7 @@ replace define V4L2_CAP_META_CAPTURE device-capabilities
> replace define V4L2_CAP_READWRITE device-capabilities
> replace define V4L2_CAP_ASYNCIO device-capabilities
> replace define V4L2_CAP_STREAMING device-capabilities
> +replace define V4L2_CAP_MC_CENTRIC device-capabilities
> replace define V4L2_CAP_DEVICE_CAPS device-capabilities
> replace define V4L2_CAP_TOUCH device-capabilities
>
> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> index 45cf7359822c..7b490fe97980 100644
> --- a/include/uapi/linux/videodev2.h
> +++ b/include/uapi/linux/videodev2.h
> @@ -460,6 +460,8 @@ struct v4l2_capability {
>
> #define V4L2_CAP_TOUCH 0x1000 /* Is a touch device */
>
> +#define V4L2_CAP_MC_CENTRIC 0x2000 /* Device require
> mc-centric hardware control */
requires
MC-centric
> +
> #define V4L2_CAP_DEVICE_CAPS0x8000 /* sets device
> capabilities field */
>
> /*
>
Regards,
Hans
[PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
As both vdev-centric and MC-centric devices may implement the
same APIs, we need a flag to allow userspace to distinguish
between them.
Signed-off-by: Mauro Carvalho Chehab
---
Documentation/media/uapi/v4l/open.rst| 7 +++
Documentation/media/uapi/v4l/vidioc-querycap.rst | 5 +
Documentation/media/videodev2.h.rst.exceptions | 1 +
include/uapi/linux/videodev2.h | 2 ++
4 files changed, 15 insertions(+)
diff --git a/Documentation/media/uapi/v4l/open.rst
b/Documentation/media/uapi/v4l/open.rst
index 64b1de047b1b..d0930fc170f0 100644
--- a/Documentation/media/uapi/v4l/open.rst
+++ b/Documentation/media/uapi/v4l/open.rst
@@ -46,6 +46,13 @@ the periferal can be used. For such devices, the
sub-devices' configuration
can be controlled via the :ref:`sub-device API `, which creates one
device node per sub-device.
+.. attention::
+
+ Devices that require **mc-centric** hardware peripheral control should
+ report a ``V4L2_MC_CENTRIC`` :c:type:`v4l2_capability` flag
+ (see :ref:`VIDIOC_QUERYCAP`).
+
+
In summary, for **MC-centric** hardware peripheral control:
- The **V4L2 device** node is responsible for controlling the streaming
diff --git a/Documentation/media/uapi/v4l/vidioc-querycap.rst
b/Documentation/media/uapi/v4l/vidioc-querycap.rst
index 12e0d9a63cd8..2b08723375bc 100644
--- a/Documentation/media/uapi/v4l/vidioc-querycap.rst
+++ b/Documentation/media/uapi/v4l/vidioc-querycap.rst
@@ -252,6 +252,11 @@ specification the ioctl returns an ``EINVAL`` error code.
* - ``V4L2_CAP_TOUCH``
- 0x1000
- This is a touch device.
+* - ``V4L2_MC_CENTRIC``
+ - 0x2000
+ - Indicates that the device require **mc-centric** hardware
+control, and thus can't be used by **v4l2-centric** applications.
+See :ref:`v4l2_hardware_control` for more details.
* - ``V4L2_CAP_DEVICE_CAPS``
- 0x8000
- The driver fills the ``device_caps`` field. This capability can
diff --git a/Documentation/media/videodev2.h.rst.exceptions
b/Documentation/media/videodev2.h.rst.exceptions
index a5cb0a8686ac..b51a575f9f75 100644
--- a/Documentation/media/videodev2.h.rst.exceptions
+++ b/Documentation/media/videodev2.h.rst.exceptions
@@ -157,6 +157,7 @@ replace define V4L2_CAP_META_CAPTURE device-capabilities
replace define V4L2_CAP_READWRITE device-capabilities
replace define V4L2_CAP_ASYNCIO device-capabilities
replace define V4L2_CAP_STREAMING device-capabilities
+replace define V4L2_CAP_MC_CENTRIC device-capabilities
replace define V4L2_CAP_DEVICE_CAPS device-capabilities
replace define V4L2_CAP_TOUCH device-capabilities
diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
index 45cf7359822c..7b490fe97980 100644
--- a/include/uapi/linux/videodev2.h
+++ b/include/uapi/linux/videodev2.h
@@ -460,6 +460,8 @@ struct v4l2_capability {
#define V4L2_CAP_TOUCH 0x1000 /* Is a touch device */
+#define V4L2_CAP_MC_CENTRIC 0x2000 /* Device require
mc-centric hardware control */
+
#define V4L2_CAP_DEVICE_CAPS0x8000 /* sets device
capabilities field */
/*
--
2.13.3
