You could replace the loop by "sleep 15" or similar, but for testing purposes, maybe it would be easier to add Xorg, the ati/radeon driver and radeon firmware "onboot", remove Xvesa from "onboot" and add the bootcode "text" to prevent tc from booting to the gui.
This would enable to you check dmesg for radeon firmware messages before issuing the "startx" command.
In /var/log/Xorg.0.log you will see that Xorg decides which drivers it thinks it could use and then tries to load them one by one before selecting the best one. This is for intel hardware, but you should see something analogous: [ 191.464] (==) Matched intel as autoconfigured driver 0
[ 191.464] (==) Matched intel as autoconfigured driver 1
[ 191.464] (==) Matched modesetting as autoconfigured driver 2
[ 191.464] (==) Matched fbdev as autoconfigured driver 3
[ 191.464] (==) Matched vesa as autoconfigured driver 4
[ 191.464] (==) Assigned the driver to the xf86ConfigLayout
[ 191.464] (II) LoadModule: "intel"
[ 191.464] (II) Loading /usr/local/lib/xorg/modules/drivers/intel_drv.so
[ 191.472] (II) Module intel: vendor="X.Org Foundation"
[ 191.472] compiled for 1.16.1, module version = 2.99.916
[ 191.472] Module class: X.Org Video Driver
[ 191.472] ABI class: X.Org Video Driver, version 18.0
[ 191.472] (II) LoadModule: "modesetting"
[ 191.473] (WW) Warning, couldn't open module modesetting
[ 191.473] (II) UnloadModule: "modesetting"
[ 191.473] (II) Unloading modesetting
[ 191.473] (EE) Failed to load module "modesetting" (module does not exist, 0)
[ 191.473] (II) LoadModule: "fbdev"
[ 191.473] (WW) Warning, couldn't open module fbdev
[ 191.473] (II) UnloadModule: "fbdev"
[ 191.473] (II) Unloading fbdev
[ 191.473] (EE) Failed to load module "fbdev" (module does not exist, 0)
[ 191.473] (II) LoadModule: "vesa"
[ 191.473] (WW) Warning, couldn't open module vesa
[ 191.473] (II) UnloadModule: "vesa"
[ 191.473] (II) Unloading vesa
[ 191.473] (EE) Failed to load module "vesa" (module does not exist, 0)
[ 191.473] (II) intel: Driver for Intel(R) Integrated Graphics Chipsets:
i810, i810-dc100, i810e, i815, i830M, 845G, 854, 852GM/855GM, 865G,
915G, E7221 (i915), 915GM, 945G, 945GM, 945GME, Pineview GM,
Pineview G, 965G, G35, 965Q, 946GZ, 965GM, 965GME/GLE, G33, Q35, Q33,
GM45, 4 Series, G45/G43, Q45/Q43, G41, B43
[ 191.473] (II) intel: Driver for Intel(R) HD Graphics: 2000-6000
[ 191.473] (II) intel: Driver for Intel(R) Iris(TM) Graphics: 5100, 6100
[ 191.473] (II) intel: Driver for Intel(R) Iris(TM) Pro Graphics: 5200, 6200, P6300
[ 191.473] (--) using VT number 2
[ 191.477] (II) intel(0): Using Kernel Mode Setting driver: i915, version 1.6.0 20080730
[ 191.478] (--) intel(0): Integrated Graphics Chipset: Intel(R) HD Graphics 4400
[ 191.479] (--) intel(0): CPU: x86-64, sse2, sse3, ssse3, sse4.1, sse4.2, avx, avx2