Created attachment 84033 [details]
Relevant bits of dmesg

My box has mgag200 primary and radeon (HD7750) secondary.  Xorg crashes on startup in do_winsys_init, which is passed fd = -1.  The crash is because drmGetVersion returns NULL.  'rmmod radeon' allows X to start (but without the radeon device).

This is Fedora 19, fully up to date.  The install disk has the same problem.

I'm not sure where fd is supposed to be set to something real, so this bug might be targeting the wrong thing.

(gdb) bt full                                                                                             [10/139]
#0  do_winsys_init (ws=0x2ff7f20) at radeon_drm_winsys.c:212
        gem_info = {gart_size = 0, vram_size = 0, vram_visible = 0}
        retval = <optimized out>
        version = <optimized out>
#1  radeon_drm_winsys_create (fd=-1) at radeon_drm_winsys.c:617
        ws = 0x2ff7f20
#2  0x00007fc2dd8fd359 in create_screen (fd=<optimized out>) at target.c:11
        radeon = <optimized out>
        screen = <optimized out>
#3  0x00007fc2ddbc5c32 in dri2_init_screen (sPriv=0x2ff7e00) at dri2.c:888
        configs = <optimized out>
        screen = 0x2ff7e90
        pscreen = <optimized out>
        throttle_ret = 0x0
#4  0x00007fc2dae2e2dd in driCreateNewScreen (scrn=0, extensions=0x7fc2df941b50 <loader_extensions>, 
    driver_configs=0x2f76700, data=0x2f76660) at ../../../../src/mesa/drivers/dri/common/drisw_util.c:70
        emptyExtensionList = {0x0}
        psp = 0x2ff7e00
#5  0x00007fc2df713b91 in __glXDRIscreenProbe (pScreen=0x2f473b0) at glxdriswrast.c:458
        driverName = 0x7fc2df72e2a6 "swrast"
        screen = 0x2f76660
#6  0x00007fc2df71315a in GlxExtensionInit () at glxext.c:355
        glxScreen = <optimized out>
        extEntry = <optimized out>
        pScreen = 0x2f473b0
        i = 0
        p = 0x7fc2df941b20 <__glXDRISWRastProvider>
        stack = <optimized out>
        glx_provided = 0
#7  0x00000000004ba1a1 in InitExtensions (argc=argc@entry=1, argv=argv@entry=0x7fff9f7860a8)
    at ../../../mi/miinitext.c:337
        i = <optimized out>
        ext = <optimized out>
#8  0x00000000004262e0 in main (argc=1, argv=0x7fff9f7860a8, envp=<optimized out>) at main.c:208
        i = <optimized out>
        alwaysCheckForInput = {0, 1}