Re: Xorg dies on my deferred I/O fb driver

On Wed, 17 Dec 2008, Ico Doornekamp wrote:

Today I wrote a simple framebuffer driver for a SPI driven LCD display
with internal memory, using the deferred I/O framework. The display is
capable of grayscale, 384x160 pixels.

My driver resembles the metronomefb driver, and seems to work using
write() and mmap() with my own test tools.

The next step would be to run Xorg/fbdev on top, but things don't seem
to simple work this way.

Xorg starts and detects te framebuffer driver, but dies with the message

  (EE) FBDEV(0): FBIOPUT_VSCREENINFO succeeded but modified mode
  (EE) FBDEV(0): mode initialization failed

I'm kind of stuck here. Any tips on how to solve or debug this one ?

On the bottom of this mail I pasted:

- fbinfo -i output
- Xorg log
- fb_fix_screeninfoa and fb_var_screeninfo from my driver

Running Xorg 1.4.2 on Linux 2.6.27.4

I guess your frame buffer device driver supports one single video mode only?

There's a bug in Xorg that doesn't like drivers that support one single video
mode only, and always return that single video mode in the FBIOPUT_VSCREENINFO
ioctl (cfr. the "FBIOPUT_VSCREENINFO succeeded but modified mode" message).

One fix is to modify your frame buffer device driver to reject all modes that
are not identical to the single supported mode.
 
Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

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