Two things could be the problem here:
- MergedFB patch, which is an old patch originating from the X.Org 6.8 days, could be wrecked in 7.1
- mga_hal support, which was broken and fixed by getting a fixed binding.h from the semi-free drivers from matrox itself

Could you try to recompile xf86-video-mga from abs, removing the patch for mga-mergedfb-xinerama? If that doesn't work out either, you could try to remove the binding patch and remove the line that adds an "USEMGAHAL 1" line to config.h. My guess is that one of these two is the problem in your case.

I have recompiled driver without mga-mergedfb-xinerama, but it did not change anything. Then I was trying to compile it without mga-mergedfb-xinerama and "USEMGAHAL 1" but all I've got is this error:

Making all in src
make[2]: Entering directory `/var/abs/x11-drivers/xf86-video-mga/src/xf86-video-mga-1.4.1/src'
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT clientlx.lo -MD -MP -MF ".deps/clientlx.Tpo" -c -o clientlx.lo clientlx.c; \
then mv -f ".deps/clientlx.Tpo" ".deps/clientlx.Plo"; else rm -f ".deps/clientlx.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT clientlx.lo -MD -MP -MF .deps/clientlx.Tpo -c clientlx.c -fPIC -DPIC -o .libs/clientlx.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_arc.lo -MD -MP -MF ".deps/mga_arc.Tpo" -c -o mga_arc.lo mga_arc.c; \
then mv -f ".deps/mga_arc.Tpo" ".deps/mga_arc.Plo"; else rm -f ".deps/mga_arc.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_arc.lo -MD -MP -MF .deps/mga_arc.Tpo -c mga_arc.c -fPIC -DPIC -o .libs/mga_arc.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_bios.lo -MD -MP -MF ".deps/mga_bios.Tpo" -c -o mga_bios.lo mga_bios.c; \
then mv -f ".deps/mga_bios.Tpo" ".deps/mga_bios.Plo"; else rm -f ".deps/mga_bios.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_bios.lo -MD -MP -MF .deps/mga_bios.Tpo -c mga_bios.c -fPIC -DPIC -o .libs/mga_bios.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dac3026.lo -MD -MP -MF ".deps/mga_dac3026.Tpo" -c -o mga_dac3026.lo mga_dac3026.c; \
then mv -f ".deps/mga_dac3026.Tpo" ".deps/mga_dac3026.Plo"; else rm -f ".deps/mga_dac3026.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dac3026.lo -MD -MP -MF .deps/mga_dac3026.Tpo -c mga_dac3026.c -fPIC -DPIC -o .libs/mga_dac3026.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dacG.lo -MD -MP -MF ".deps/mga_dacG.Tpo" -c -o mga_dacG.lo mga_dacG.c; \
then mv -f ".deps/mga_dacG.Tpo" ".deps/mga_dacG.Plo"; else rm -f ".deps/mga_dacG.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dacG.lo -MD -MP -MF .deps/mga_dacG.Tpo -c mga_dacG.c -fPIC -DPIC -o .libs/mga_dacG.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dga.lo -MD -MP -MF ".deps/mga_dga.Tpo" -c -o mga_dga.lo mga_dga.c; \
then mv -f ".deps/mga_dga.Tpo" ".deps/mga_dga.Plo"; else rm -f ".deps/mga_dga.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dga.lo -MD -MP -MF .deps/mga_dga.Tpo -c mga_dga.c -fPIC -DPIC -o .libs/mga_dga.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dh.lo -MD -MP -MF ".deps/mga_dh.Tpo" -c -o mga_dh.lo mga_dh.c; \
then mv -f ".deps/mga_dh.Tpo" ".deps/mga_dh.Plo"; else rm -f ".deps/mga_dh.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_dh.lo -MD -MP -MF .deps/mga_dh.Tpo -c mga_dh.c -fPIC -DPIC -o .libs/mga_dh.o
if /bin/sh ../libtool --tag=CC --mode=compile i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_driver.lo -MD -MP -MF ".deps/mga_driver.Tpo" -c -o mga_driver.lo mga_driver.c; \
then mv -f ".deps/mga_driver.Tpo" ".deps/mga_driver.Plo"; else rm -f ".deps/mga_driver.Tpo"; exit 1; fi
i686-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I. -I.. -DXFree86Server -DIN_MODULE -DXFree86Module -DXFree86LOADER -I/usr/include/xorg -I/usr/include/drm -I/usr/include/X11/dri -march=i686 -O2 -pipe -I/usr/include/X11/extensions -MT mga_driver.lo -MD -MP -MF .deps/mga_driver.Tpo -c mga_driver.c -fPIC -DPIC -o .libs/mga_driver.o
mga_driver.c: In function 'MGAFillModeInfoStruct':
mga_driver.c:2678: error: 'MGAMODEINFO_FLATPANEL1' undeclared (first use in this function)
mga_driver.c:2678: error: (Each undeclared identifier is reported only once
mga_driver.c:2678: error: for each function it appears in.)
make[2]: *** [mga_driver.lo] Error 1
make[2]: Leaving directory `/var/abs/x11-drivers/xf86-video-mga/src/xf86-video-mga-1.4.1/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/abs/x11-drivers/xf86-video-mga/src/xf86-video-mga-1.4.1'
make: *** [all] Error 2

Could you remove the src directory before retrying? could be that hal support is still enabled. Maybe there's a switch in ./configure to disable it these days.

I did remove src dir. Still can't compile it (the same error). There is no switch to enable or disable hal in ./configure script.

I was able to compile without both patches and removing the line that adds the define to config.h.

Finally I managed to compile it as You said No patches no USEMGAHAL 1 but it still doesn't work.

Can't see any weird things in the logs. You might want to try mga_hal, which you should build as described in the last forum post I did in this thread:
http://bbs.archlinux.org/viewtopic.php?t=25021

Another option is using gtf to generate modelines, but looking at your logs that doesn't help much I think.

I managed to compile mga_hal. This time seems to be no synch. problem however I get this error:

(==) Using config file: "/etc/X11/xorg.conf"

X: symbol lookup error: /usr/lib/xorg/modules/drivers/mga_drv.so: undefined symbol: MGAGetBOARDHANDLESize
XIO: fatal IO error 104 (Connection reset by peer) on X server ":0.0"
after 0 requests (0 known processed) with 0 events remaining.

I try the original mga driver from current, with or without patches, but it still doesn't work.

Try without the mga_hal module again, this time with the latest mga driver. There have been some updates to it, but I can't tell you if they fix your problems for sure.

Gdm starts then fails, after several unsuccessful restart, xorg reports a error message. Doesn't try if startx can start x windows, have to wait to see and report lately when I go home.

I haven't got mga_hal for Xorg 7.1 but mga driver works fine now.
Thx

Could you post your xorg.conf here, thanks. The following is mine.

After installing mesa, it works. I think the bug can be closed. However why I have to install mesa is clueless.

Well... mga seems to work fine, but I've just found, that Direct Rendering doesn't work for some reason.

[kat@myhost ~]$ glxinfo
name of display: :0.0
display: :0 screen: 0
direct rendering: No
server glx vendor string: SGI
server glx version string: 1.2
[.....]
OpenGL vendor string: Mesa project: www.mesa3d.org
OpenGL renderer string: Mesa GLX Indirect
OpenGL version string: 1.2 (1.5 Mesa 6.5.1)
[.....]

If the Direct Rendering problem isn't a result of incorrect configuration,  FS#5384  is not ready to be closed.

What does LIBGL_DEBUG=1 glxinfo give?

mga_dri.so is missing.

name of display: :0.0
libGL error: dlopen /usr/lib/xorg/modules/dri/mga_dri.so failed (/usr/lib/xorg/modules/dri/mga_dri.so: cannot open shared object file: No such file or directory)
libGL error: unable to load driver: mga_dri.so
display: :0 screen: 0
direct rendering: No

Is it part of the matrox driver?

OK, my mistake. I took them out so I could work on mga_hal compilation, didn't add it back in after that and used that PKGBUILD as base for xf86-video-mga-1.4.2-1. A fixed driver with DRI drivers will appear in a little while.

THX.

The latest mga driver brings DRI, but all OpenGL app. couses computer hangs.

xf86-video-mga 1.4.2 was supposed to fix that.

Well... it did not :)