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[PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices

Started byMauro Carvalho Chehab <mchehab@s-opensource.com>
First post2017-08-26 14:00 +0200
Last post2017-08-28 15:30 +0200
Articles 3 — 2 participants

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  [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-08-26 14:00 +0200
    Re: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric  devices Hans Verkuil <hverkuil@xs4all.nl> - 2017-08-28 11:50 +0200
      V4L2 device node centric - Was: [PATCH v4 6/7] media: videodev2:  add a flag for MC-centric  devices Mauro Carvalho Chehab <mchehab@s-opensource.com> - 2017-08-28 15:30 +0200

#1720649 — [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices

FromMauro Carvalho Chehab <mchehab@s-opensource.com>
Date2017-08-26 14:00 +0200
Subject[PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
Message-ID<uiHUS-Iu-19@gated-at.bofh.it>
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 <mchehab@s-opensource.com>
---
 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 <subdev>`, 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``
       - 0x10000000
       - This is a touch device.
+    * - ``V4L2_MC_CENTRIC``
+      - 0x20000000
+      - 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``
       - 0x80000000
       - 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                  0x10000000  /* Is a touch device */
 
+#define V4L2_CAP_MC_CENTRIC             0x20000000  /* Device require mc-centric hardware control */
+
 #define V4L2_CAP_DEVICE_CAPS            0x80000000  /* sets device capabilities field */
 
 /*
-- 
2.13.3

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#1721447 — Re: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices

FromHans Verkuil <hverkuil@xs4all.nl>
Date2017-08-28 11:50 +0200
SubjectRe: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
Message-ID<ujoQa-3WH-19@gated-at.bofh.it>
In reply to#1720649
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 <mchehab@s-opensource.com>
> ---
>  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 <subdev>`, 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``
>        - 0x10000000
>        - This is a touch device.
> +    * - ``V4L2_MC_CENTRIC``
> +      - 0x20000000
> +      - 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``
>        - 0x80000000
>        - 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                  0x10000000  /* Is a touch device */
>  
> +#define V4L2_CAP_MC_CENTRIC             0x20000000  /* Device require mc-centric hardware control */

requires
MC-centric

> +
>  #define V4L2_CAP_DEVICE_CAPS            0x80000000  /* sets device capabilities field */
>  
>  /*
> 

Regards,

	Hans

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#1721621 — V4L2 device node centric - Was: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices

FromMauro Carvalho Chehab <mchehab@s-opensource.com>
Date2017-08-28 15:30 +0200
SubjectV4L2 device node centric - Was: [PATCH v4 6/7] media: videodev2: add a flag for MC-centric devices
Message-ID<ujsh5-665-43@gated-at.bofh.it>
In reply to#1721447
Em Mon, 28 Aug 2017 11:41:58 +0200
Hans Verkuil <hverkuil@xs4all.nl> 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

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