RE: Tentative agenda for Helsinki mini-summit

On Thu, 27 May 2010, Pawel Osciak wrote:

Hi,

quoted

Guennadi Liakhovetski wrote:

No idea whether this is a worthy and suitable topic for this meeting, but:

V4L(2) video output vs. framebuffer.

How about a v4l2-output - fbdev translation layer? You write a v4l2-output
driver and get a framebuffer device free of charge... TBH, I haven't given
this too much of a thought, but so far I don't see anything that would
make this impossible in principle. The video buffer management is quite
different between the two systems, but maybe we can teach video-output
drivers to work with just one buffer too? Anyway, feel free to tell me why
this is an absolutely impossible / impractical idea;)

We also use v4l2-outputs for our display interfaces and for that we have
v4l2-subdevices in a framebuffer driver. Although we have had no need for
such a translation layer per se up to now, the idea seems interesting.

Interesting, but sorry, don't quite understand "we use v4l2-outputs" and 
"in a framebuffer driver" - so, is it a framebuffer (/dev/fbX) or a v4l2 
output device driver or both? Which driver is this? Is it already in the 
mainline?

I would definitely be interested in a general discussion about framebuffer
driver - v4l2 output device interoperability though and can share our
experience in this field.

Yes, please, do, it would be very much appreciated!

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Guennadi Liakhovetski [off-list ref] wrote:
On Thu, 27 May 2010, Pawel Osciak wrote:

quoted

Hi,

quoted

Guennadi Liakhovetski wrote:

No idea whether this is a worthy and suitable topic for this meeting, but:

V4L(2) video output vs. framebuffer.

How about a v4l2-output - fbdev translation layer? You write a v4l2-output
driver and get a framebuffer device free of charge... TBH, I haven't given
this too much of a thought, but so far I don't see anything that would
make this impossible in principle. The video buffer management is quite
different between the two systems, but maybe we can teach video-output
drivers to work with just one buffer too? Anyway, feel free to tell me why
this is an absolutely impossible / impractical idea;)

We also use v4l2-outputs for our display interfaces and for that we have
v4l2-subdevices in a framebuffer driver. Although we have had no need for
such a translation layer per se up to now, the idea seems interesting.

Interesting, but sorry, don't quite understand "we use v4l2-outputs" and
"in a framebuffer driver" - so, is it a framebuffer (/dev/fbX) or a v4l2
output device driver or both? Which driver is this? Is it already in the
mainline?

It's the (mostly) standard s3c-fb driver with a v4l2-subdev video interface
added. A separate v4l2 output device driver uses that interface to communicate
with the framebuffer driver, as some setup is required on both parts.

Those operations cannot be performed from userspace as they have to be
synchronized in interrupts.

Best regards
--
Pawel Osciak
Linux Platform Group
Samsung Poland R&D Center