Fails to run on -ati: No connected DRM encoder

After installing the pieces listed below from the staging ppa, mir failed to start up.

Note that the version of mesa is from the raring archive rather than the PPA. The versions of mesa in the PPA currently are either unavailable or failed to build.

On this hardware, I had mir running earlier, although the screen was entirely corrupted.

[Hardware]
redwood (1002:68d8) xserver-xorg-video-ati,fglrx-installer

[Packages and Processes]
Component Version Running
mir 0.0.1-0ubuntu5 [FAIL]
lightdm 1.4.0-0ubuntu2+mir4 [OK]
mesa 9.0.2-0ubuntu1
xorg-server 2:1.13.1.901-0ubuntu2+xmir1 [FAIL]
-ati 1:7.0.0-0ubuntu1+xmir2
-intel 2:2.20.19-0ubuntu1+xmir1
-nouveau 1:1.0.6-0ubuntu1
-fglrx (none)
-nvidia (none)
-tegra

[Configuration]
[SeatDefaults]
#autologin-guest=false
#autologin-user=bryce
#autologin-user-timeout=0
#autologin-session=lightdm-autologin
user-session=ubuntu
greeter-session=unity-greeter
type=mir

[mir.log]
ERROR: /build/buildd/mir-0.0.1/src/graphics/gbm/gbm_display_helpers.cpp(180): Throw in function void mir::graphics::gbm::helpers::KMSHelper::setup(const mir::graphics::gbm::helpers::DRMHelper&)
Dynamic exception type: boost::exception_detail::clone_impl<boost::exception_detail::error_info_injector<std::runtime_error> >
std::exception::what: No connected DRM encoder found