On 03/03/2017 03:06 PM, Russell King - ARM Linux wrote:
On Thu, Mar 02, 2017 at 06:02:57PM +0200, Sakari Ailus wrote:
Hi Steve,
On Wed, Feb 15, 2017 at 06:19:16PM -0800, Steve Longerbeam wrote:
v4l2_pipeline_inherit_controls() will add the v4l2 controls from
all subdev entities in a pipeline to a given video device.
Signed-off-by: Steve Longerbeam <steve_longerbeam@xxxxxxxxxx>
---
drivers/media/v4l2-core/v4l2-mc.c | 48 +++++++++++++++++++++++++++++++++++++++
include/media/v4l2-mc.h | 25 ++++++++++++++++++++
2 files changed, 73 insertions(+)
diff --git a/drivers/media/v4l2-core/v4l2-mc.c b/drivers/media/v4l2-core/v4l2-mc.c
index 303980b..09d4d97 100644
--- a/drivers/media/v4l2-core/v4l2-mc.c
+++ b/drivers/media/v4l2-core/v4l2-mc.c
@@ -22,6 +22,7 @@
#include <linux/usb.h>
#include <media/media-device.h>
#include <media/media-entity.h>
+#include <media/v4l2-ctrls.h>
#include <media/v4l2-fh.h>
#include <media/v4l2-mc.h>
#include <media/v4l2-subdev.h>
@@ -238,6 +239,53 @@ int v4l_vb2q_enable_media_source(struct vb2_queue *q)
}
EXPORT_SYMBOL_GPL(v4l_vb2q_enable_media_source);
+int __v4l2_pipeline_inherit_controls(struct video_device *vfd,
+ struct media_entity *start_entity)
I have a few concerns / questions:
- What's the purpose of this patch? Why not to access the sub-device node
directly?
What tools are in existance _today_ to provide access to these controls
via the sub-device nodes?
v4l-tools doesn't last time I looked - in fact, the only tool in v4l-tools
which is capable of accessing the subdevices is media-ctl, and that only
provides functionality for configuring the pipeline.
So, pointing people at vapourware userspace is really quite rediculous.
Hi Russell,
Yes, that's a big reason why I added this capability. The v4l2-ctl
tool won't accept subdev nodes, although Philipp Zabel has a quick hack
to get around this (ignore return code from VIDIOC_QUERYCAP).
The established way to control video capture is through the main video
capture device, not through the sub-devices. Yes, the controls are
exposed through sub-devices too, but that does not mean that is the
correct way to access them.
The v4l2 documentation (Documentation/media/kapi/v4l2-controls.rst)
even disagrees with your statements. That talks about control
inheritence from sub-devices to the main video device, and the core
v4l2 code provides _automatic_ support for this - see
v4l2_device_register_subdev():
/* This just returns 0 if either of the two args is NULL */
err = v4l2_ctrl_add_handler(v4l2_dev->ctrl_handler, sd->ctrl_handler, NULL);
which merges the subdev's controls into the main device's control
handler.
Actually v4l2_dev->ctrl_handler is not of much use to me. This will
compose a list of controls from all registered subdevs, i.e. _all
possible controls_.
What v4l2_pipeline_inherit_controls() does is compose a list of
controls that are reachable and available in the currently configured
pipeline.
Steve
So, (a) I don't think Steve needs to add this code, and (b) I think
your statements about not inheriting controls goes against the
documentation and API compatibility with _existing_ applications,
and ultimately hurts the user experience, since there's nothing
existing today to support what you're suggesting in userspace.
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