[Libdlo] Frame Buffer with UDLFB broken since disabling defio

[Bernie Thompson]

Hi Justin,

Unfortunately, there are problems with udlfb+defio that are still
unresolved -- primarily: 1) pages accumulate which no longer trigger
writes, building up dead lines on the screen 2) with 2+ devices,
updates to one bizarrely affect the other and 3) pages not being
present when the driver is handed them to process - causing kernel
oops.

So even though the defio support is tantalizing close, I've been
completely stumped by these problems (I don't see any errors in udlfb
to cause them, and don't know Linux MMU handling well enough to
re-review all of defio) -- and they're severe enough that it's not
good to have "normal" users stumble on them.

But - it's easy enough to turn the support back on.  Just remove that
#undef CONFIG_FB_DEFERRED_IO
line in the code (visible in the commit diff in your link below).

Would love to have help from anywhere on figuring out the source of
the problems.  Getting defio back on by default would be great, as
it's the only clean way to support "normal" USB-unaware fbdev clients
who just mmap the framebuffer.

Best wishes,
Bernie

On Mon, Apr 19, 2010 at 5:12 AM, Justin Hammond <justin at dynam.ac> wrote:
> Hi,
> I'm using a Mimi 720 and saw that there was a recent commit to enable DPMS.
> I've upgraded, but all of a sudden my QT Embeded application has stopped
> working. I've also check with other apps, such as mplayer and that is also
> not working.
>
> I've narrowed it down to this commit:
> http://git.plugable.com/gitphp/index.php?p=udlfb&a=commit&h=dba564a4a31bdf62a0e9768cbcdcce4edf85618a
>
> Previous versions worked fined with both my app and mplayer. On module load,
> I get the green screen.... :)
>
> Not sure what the defio code has disabled... but would be nice to get it
> working again...
>
> (btw, as far as I can tell, the DPMS code works fine. "echo 1 >
> /sys/class/graphics/blank" turns off the monitor... 0 turns it back to
> greenscreen!)
>
> (mplayer command line: mplayer -vo fbdev2:/dev/fb1 /home/movies/IceAge-2.avi
> )
>
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