Hi Mauro,
Mauro Carvalho Chehab wrote:
Em 10-06-2012 17:22, Sakari Ailus escreveu:
Hi Mauro,
Here are two V4L2 API cleanup patches; the first removes __user from
videodev2.h from a few places, making it possible to use the header file
as such in user space, while the second one changes the
v4l2_buffer.input field back to reserved.
The following changes since commit 5472d3f17845c4398c6a510b46855820920c2181:
[media] mt9m032: Implement V4L2_CID_PIXEL_RATE control (2012-05-24
09:27:24 -0300)
are available in the git repository at:
ssh://linuxtv.org/git/sailus/media_tree.git media-for-3.6
Sakari Ailus (2):
v4l: Remove __user from interface structure definitions
v4l: drop v4l2_buffer.input and V4L2_BUF_FLAG_INPUT
Indeed, no drivers use V4L2_BUF_FLAG_INPUT, although I think this should be
used there, for some devices.
There are several surveillance boards (mostly bttv boards, but there are
also cx88 and saa7134 models in the market) where the same chip is used
by up to 4 cameras. What software does is to switch the video input
to sample one of those cameras on a given frequency (1/60Hz or 1/30Hz),
in order to collect the streams for the 4 cameras.
Without an input field there at the buffer metadata, it might happen that
software would look into the wrong input.
That's said, considering that:
1) no driver is currently filling buffer queue with its "inputs" field,
this flag is not used anywhere;
2) an implementation for input switch currently requires userspace to tell
Kernel to switch to the next input, with is racy;
3) a model where the Kernel itself would switch to the next input would
require some Kernelspace changes.
I agree that we can just remove this bad implementation. If latter needed,
we'll need to not only reapply this patch but also to add a better way to
allow time-sharing the same video sampler with multiple inputs.
So, I'll apply this patch.
Thanks!
There was a discussion between Ezequiel and Hans that in my
understanding led to a conclusion there's no such use case, at least one
which would be properly supported by the hardware. (Please correct me if
I'm mistaken.)
<URL:http://www.spinics.net/lists/linux-media/msg48474.html>
So if we ever get such hardware then we could start rethinking it. :-)
Cheers,
--
Sakari Ailus
sakari.ailus@xxxxxx
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