Bug#389433: Probable fix for fbdev shadow framebuffer issues
On Fri, 2006-12-29 at 13:04 +0000, Robert de Bath wrote:
> > That's bug #338241. I'm pondering changing the fbdev driver to default
> > to 32bpp though.
> Well I suppose 32bpp is more likely with modern hardware.
FWIW, xf86-video-fbdev 0.3.1 defaults to 32.
> Still even if you can't easily get fb_var_screeninfo.bits_per_pixel as
> your default a big fat warning that they don't match and how to fix it
> would be in order IMO.
I don't know any way to determine that's the specific reason for the
FBIOPUT_VSCREENINFO ioctl failing. If there are any framebuffer devices
that accept 24 bpp but not 32 bpp, I guess the fbdev driver could check
for that, but I don't particularly feel like spending more time on this
right now.
> > I noticed that, but it's more likely a bug in vesafb. As the log
> > indicates, the fbdev driver actually queries the framebuffer device on
> > the usability of each mode.
>
> I've had a look at the kernel code ...
> Well it seems that the vesafb doesn't have an fb_check_var function to
> call so the FBIOPUT_VSCREENINFO ioctl is defined by fbmem.c to be the
> same as FBIOGET_VSCREENINFO.
>
> This is actually reasonable, it's trying to tell you the closest mode
> to the one you asked for. But X will have to check that the mode it gets
> back is "the same" as the one it asked for and reject it if not.
> (Especially if the returned mode is SMALLER than the request!)
X considers modes to be different even if only a single parameter
differs, so I've changed fbdevhw to report failure in that case in
http://gitweb.freedesktop.org/?p=xorg/xserver.git;a=commitdiff;h=f6815cb68b0f6698497348fc6e4214dacef33b95
> Also the TEST function doesn't look like it's implemented properly in
> all the drivers; I'd make sure you 'GET' the original setup and 'TEST'
> it after you've tested all your configured modes!
I don't understand what you're saying here, please elaborate.
> > ...
>
> But back to the beginning; the bug this report was opened for looks fixed
> to me.
Yes, so please follow up to the linux-fbdev-devel list (or another
appropriate place) only.
--
Earthling Michel Dänzer | http://tungstengraphics.com
Libre software enthusiast | Debian, X and DRI developer
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