Radeon MergedFB & forcing constant DPI

[Zak]

Hi chaps,

I'm using the radeon driver in MergedFB mode on a laptop.  I have two 
MetaModes set up: 1024x768 (clone) and 1024x768-1280x1024 (merged).  I 
frequently add and remove the second monitor, and running "xrandr -s 
<N>" neatly toggles the setup between 2304x1024/merge and  
1024x768/clone at runtime.  (It throws my icons around a bit, but 
that's probably KDE's fault, and it's way better than having to restart 
X every time I add/remove the monitor, or have the second half of the 
desktop present-but-unusable when there's no external monitor.)

This setup works great except that whenever I do "xrandr -s <N>", X also 
changes the DPI.  Running xdpyinfo in the external-monitor-present 
setup that X starts in, I get the expected 100x100 DPI, but in the 
standalone setup I get 44x75 DPI.  Apps started with this DPI obviously 
have fairly unreadable fonts.

I've tried both:
 Option          "MergedDPI" "100 100"
and the "-dpi 100" option to the X server, but neither setting survives 
across an xrandr change.

A bit of Googling says this is a known, old, open bug:
  https://bugs.freedesktop.org/show_bug.cgi?id=692

There also appears to be a recent workaround option "ConstantDPI" in the 
sisfb implementation of MergedFB:
  http://www.winischhofer.at/linuxsispart2.shtml#constantdpi
but there's no trace of this option in the radeon driver (as far as I 
can see), no mention of it anywhere but on that page, and no mention of 
any plans to implement it that I can find.

So, I guess my questions are:

1. Are there any plans to implement the same fix in the radeon driver - 
or if it's a bug in xrandr, any plans to fix the bug there?

2. Are there any workarounds, like different ways to set up MergedFB, or 
any way to set the DRI at runtime?

3. Am I asking in the right place?

I'm using X.org 6.9.0 (Debian's xserver-xorg package, version 
6.9.0.dfsg.1-4).

Thanks in advance,

Isaac Wilcox