Display DPI wrongly calculated by driver

== Problem: ==

Wrong DPI calculated (causes too small fonts in browsers and apps, messed up display form factors in video players)

DPI as seen in xorg.log:

(II) RADEON(0): Output VGA-1 using initial mode 1280x800
after xf86InitialConfiguration
(**) RADEON(0): Display dimensions: (295, 225) mm
(**) RADEON(0): DPI set to (110, 135)

It makes no sense, the horizontal DPI is correct, but the vertical DPI is way off. WAY off. DPI should be closer to ~110 and ~90.3 (vertical DPI)

But that's not it. More inconsistencies. DPI as seen in xdpyinfo:

screen #0:
  dimensions: 1280x800 pixels (338x211 millimeters)
  resolution: 96x96 dots per inch

Even more inconsistencies: Screen dimensions as seen in xrandr:

VGA-1 connected 1280x800+0+0 (normal left inverted right) 0mm x 0mm

In summary:

resolution 1280 800
dimensions mm 295 225
dpm 4.34 3.56
correct dpi 110.21 90.31
RADEON dpi 110 135
xrandr dpi inf inf
xdpyinfo 96 96

I think KDE is picking up on the xdpyinfo DPI to draw its fonts, based on (my unscientific observation of) the relative font size.

==Extra symptoms:==

Flickers at the start of my KDE session. Consistent with the flickers produced by xrandr. I Understand it's produced by displayconfig-restore in kde-guidance:

/etc/X11/Xsession.d/40guidance-displayconfig_restore

==Things to know==

Card: ATI Radeon Mobility 7000-M

Driver: radeon

Old monitor (VESA DDC supported, disabled in xorg.conf)

NoDDC in xorg.conf Device section

DisplaySize 295 225 setup manually to true screen dimensions in xorg.conf Monitor section

PreferredMode 1280x800 in Monitor section