Re: Questions about fbdriver integration

[Ico Doornekamp <fbdev@zevv.nl>]

* On 2007-11-25 Geert Uytterhoeven <geert@linux-m68k.org> wrote  :

> On Sat, 24 Nov 2007, Ico Doornekamp wrote:
> > I have just finished writing a framebuffer driver for a LCD display
> > connected to our embedded system (monochrome, 128x64, GPIO driven).
> > It's very similar to the hecubafb driver, and uses deferred IO. I've
> > included some of the drivers properties at the end of this mail.  Things
> > works fine when displaying images by doing write()s to /dev/fb0, so this
> > part seems to be ok.
> > 
> > I hope some of the regulars on this list can clear up some issues
> > I've run into when using this driver:
> > 
> > - My next step as to redirect the linux console to this framebuffer
> >   device. I've configured the kernel for framebuffer console, and when
> >   loading the fbcon module, the message 
> >     
> >      Console: switching to mono frame buffer device 16x4" 
> >      
> >   appears, and
> > 
> >      cat /sys/class/vtconsole/vtcon1/name -> (M) frame buffer device
> >      cat /sys/class/vtconsole/vtcon1/bind -> 1
> >   
> >   This seems just fine to me, but however, no output appears on the
> >   display: just a blank screen. 
> > 
> >   It seems that the console is doing *something*, since my driver gets
> >   triggered by the deferred IO every 200msec (blinking cursor?), problem
> >   is that the data arriving in my driver is all zeroes!
> 
> Fbcon writes to the memory at fb_info.screen_base.

That is what I expected. I'll have to do a bit more debugging here then.

> > - The other question is more a userspace issue: I was hoping to use the
> >   xorg fbdev server on my dislay, but unfortunately this does not seem
> >   to support 1 bit depth displays :
> > 
> >     (EE) FBDEV(0): unsupported number of bits per pixel: 1
> > 
> >   Is there a way to make X work on 1-bit fb devices, or am I out of luck
> >   here ?
> 
> The old XF86_FBDev (from XFree86 3.x) definitely works with monochrome.
> I expect (but never tried) KDrive also to support it.
> 
> It's a pity many frame buffer organizations were dropped in Xorg.

It is, yes. I'll give Kdrive a try, or as an alternative I can make my
framebuffer 8-bit greycale instead of monochrome, with a simple
threshold. I'll be using simple monochrome apps with some text only, so
that will probably be sufficient.

Thanks,

Ico

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