2009. 9. 12., 오전 7:21, Hans Verkuil 작성:
Hi all,
I've started this as a new thread to prevent polluting the
discussions of the
media controller as a concept.
First of all, I have no doubt that everything that you can do with
an ioctl,
you can also do with sysfs and vice versa. That's not the problem
here.
The problem is deciding which approach is the best.
What is sysfs? (taken from http://lwn.net/Articles/31185/)
"Sysfs is a virtual filesystem which provides a userspace-visible
representation
of the device model. The device model and sysfs are sometimes
confused with each
other, but they are distinct entities. The device model functions
just fine
without sysfs (but the reverse is not true)."
Currently both a v4l driver and the device nodes are all represented
in sysfs.
This is handled automatically by the kernel.
Sub-devices are not represented in sysfs since they are not based on
struct
device. They are v4l-internal structures. Actually, if the subdev
represents
an i2c device, then that i2c device will be present in sysfs, but
not all
subdevs are i2c devices.
Should we make all sub-devices based on struct device? Currently
this is not
required. Doing this would probably mean registering a virtual bus,
then
attaching the sub-device to that. Of course, this only applies to
sub-devices
that represent something that is not an i2c device (e.g. something
internal
to the media board like a resizer, or something connected to GPIO
pins).
If we decide to go with sysfs, then we have to do this. This part
shouldn't
be too difficult to implement. And also if we do not go with sysfs
this might
be interesting to do eventually.
The media controller topology as I see it should contain the device
nodes
since the application has to know what device node to open to do the
streaming.
It should also contain the sub-devices so the application can
control them.
Is this enough? I think that eventually we also want to show the
physical
connectors. I left them out (mostly) from the initial media
controller proposal,
but I suspect that we want those as well eventually. But connectors
are
definitely not devices. In that respect the entity concept of the
media
controller is more abstract than sysfs.
However, for now I think we can safely assume that sub-devices can
be made
visible in sysfs.
Hans,
First of all I'm very sorry that I had not enough time to go through
your new RFC. I'll checkout right after posting this mail.
I think this is a good approach and I also had in my mind that sysfs
might be a good method if we could control and monitor through this.
Recalling memory when we had a talk in San Francisco, I was frustrated
that there is no way to catch events from sort of sub-devices like
lens actuator (I mean pizeo motors in camera module). As you know lens
actuator is an extremely slow device in comparison with common v4l2
devices we are using and we need to know whether it has succeeded or
not in moving to expected position.
So I considered sysfs and udev as candidates for catching events from
sub-devices. events like success/failure of lens movement, change of
status of subdevices.
Does anybody experiencing same issue? I think I've seen a lens
controller driver in omap3 kernel from TI but not sure how did they
control that.
My point is that we need a kind of framework to give and event to user
space and catching them properly just like udev does.
Cheers,
Nate
=
DongSoo, Nathaniel Kim
Engineer
Mobile S/W Platform Lab.
Digital Media & Communications R&D Centre
Samsung Electronics CO., LTD.
e-mail : dongsoo.kim@xxxxxxxxx
dongsoo45.kim@xxxxxxxxxxxxx
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