Hi Hans,
Le 04/13/12 07:03, Hans Verkuil a écrit :
You both hit the main problem of the CEC support: how to implement the API.
Well, the API that I propose here [1] is quite simple:
- a kernel-side API for defining CEC adapters drivers
- a character device with an ioctl() control path and read/write/poll
data-path
[1]: https://github.com/ffainelli/linux-hdmi-cec
Cisco's work on CEC has been stalled as we first want to get HDMI support in
V4L. Hopefully that will happen in the next few months. After that we will
resume working on the CEC API.
Well, I don't think that tighting HDMI into V4L is such a good idea
either. HDMI is also a separate bus and deserves its own subsystem and
even subsystems (audio, video, HDCP, CEC). For instance, the STB I am
working with does not use the V4L API at all, however, I would like to
be able to integrate within the Linux HDMI stack once there, think about
nvidia's driver too.
I can understand that you want to hold on your efforts on CEC while you
want to get HDMI in, but don't make it entirely driven by Cisco and
accept the community feedback.
Regards,
Hans
On Thursday, April 12, 2012 22:36:55 Oliver Schinagl wrote:
Since a lot of video cards dont' support CEC at all (not even
connected), don't have hdmi, but work perfectly fine with dvi->hdmi
adapters, CEC can be implemented in many other ways (think media centers)
One such exammple is using USB/Arduino
http://code.google.com/p/cec-arduino/wiki/ElectricalInterface
Having an AVR with v-usb code and cec code doesn't look all that hard
nor impossible, so one could simply have a USB plug on one end, and an
HDMI plug on the other end, utilizing only the CEC pins.
This would make it more something like LIRC if anything.
On 04/12/12 17:24, Florian Fainelli wrote:
Hi Hans, Martin,
Sorry to jump in so late in the HDMI-CEC discussion, here are some
comments from my perspective on your proposal:
- the HDMI-CEC implementation deserves its own bus and class of devices
because by definition it is a physical bus, which is even electrically
independant from the rest of the HDMI bus (A/V path)
- I don't think it is a good idea to tight it so closely to v4l, because
one can perfectly have CEC-capable hardware without video, or at least
not use v4l and have HDMI-CEC hardware
- it was suggested to use sockets at some point, I think it is
over-engineered and should only lead
- processing messages in user-space is definitively the way to go, even
input can be either re-injected using an uinput driver, or be handled in
user-space entirely, eventually we might want to install "filters" based
on opcodes to divert some opcodes to a kernel consumer, and the others
to an user-space one
Right now, I have a very simple implementation that I developed for the
company I work for which can be found here:
https://github.com/ffainelli/linux-hdmi-cec
It is designed like this:
1) A core module, which registers a cec bus, and provides an abstraction
for a CEC adapter (both device& driver):
- basic CEC adapter operations: logical address setting, queueing
management
- counters, rx filtering
- host attaching/detaching in case the hardware is capable of
self-processing CEC messages (for wakeup in particular)
2) A character device module, which exposes a character device per CEC
adapter and only allows one consumer at a time and exposes the following
ioctl's:
- SET_LOGICAL_ADDRESS
- RESET_DEVICE
- GET_COUNTERS
- SET_RX_MODE (my adapter can be set in a promiscuous mode)
the character device supports read/write/poll, which are the prefered
ways for transfering/receiving data
3) A CEC adapter implementation which registers and calls into the core
module when receiving a CEC message, and which the core module calls in
response to the IOCTLs described below.
At first I thought about defining a generic netlink family in order to
allow multiple user-space listeners receive CEC messages, but in the end
having only one consumer per adapter device is fine by me and a more
traditionnal approach for programmers.
I am relying on external components for knowing my HDMI physical address.
Hope this is not too late to (re)start the discussion on HDMI-CEC.
Thank you very much.
--
Florian
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