Re: [directfb-users] DirectFB without FBDev

On Wed, May 28, 2008 at 2:07 PM, Denis Oliver Kropp [off-list ref] wrote:

Brian G. Rhodes wrote:

quoted

quoted

Furthermore, the pan_display functionality could be enhanced to allow
a kernel side queue
for frame accurate display of several buffers, e.g. video playback
with five or more buffers
pre-rendered. A frame/sync counter and some new flags would be enough
to be added for this.
  Ville Syrjala once did an extension like FBIO_FLIP or similar, maybe
he can elaborate.

I'm also seeing the need to have one pool of memory used by different
frame buffer devices
or some other way to support multiple layers without statically
partitioning memory that could
be managed more intelligently.

And how about such capabilities like layer opacity, alpha ramps...?

I know all this was not required to run the kernel based terminal
emulation that the frame
buffer device has been invented for :)

I don't think the solution to abstracting access to multiple hardware
planes which can be located in at dynamic memory addresses to be
implemented by adding complexity to the framebuffer driver.  It is
supposed to be just a dumb chunk of memory and storage for hardware
timings.

Adding the byte offset and pitch fits into this as well and would save
it from being removed from DirectFB.

quoted

Considering video, and the amount of data which has to be shuffled
around for higher resolution/bitrate files it does not make sense to
require sending rendered frames off directly to a framebuffer device.

I was not talking about copying any data back and forth, but just keep
a queue of start addresses assigned to future sync counters, being taken
care of in IRQs.

quoted

It is too inefficient and in cases with hardware-assist (other than
coprocessors), likely unnecessary.  The answer probably isn't using
Video4Linux directly either.  Perhaps a DirectFB kernel component which
can standardize an interface and provide a better architecture than v4l2
does.  An application where, as mentioned above, you are using video
memory for multiple buffers as a implementation for queuing seems too
specialized to me to ever be done in a linuxfb driver.

It's not special regarding the hardware. Every driver with an interrupt
handler could support it.

quoted

Has any thought been given to designing a DirectFB kernel-space
component which abstracts that access at the kernel level?  Seems to me
that it would make direct interaction from directfb with specialized
hardware much easier.

I don't think a new kernel graphics interface should be added, instead using
UIO to access MMIO, DMA and IRQs would be enough and implement most of the
graphics driver in user space. Downside is to loose the kernel console which
you usually don't need on an embedded device...

For acceleration and DMA/IRQ based programming, I still need to check if a
user space approach would be enough. So far I always handled IRQs in kernel
space for timing/performance reasons...

As you may or may not be aware, the drm is slowly getting modesetting
support including support for multiple crtcs and outputs and better
memory management.  Development is currently focusing on intel, but
AMD support will follow soon.  It even provides a legacy fbdev compat
layer.

http://cgit.freedesktop.org/mesa/drm/log/?h=modesetting-101

Alex

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