commit cc47270236e07a084da0b302b4b14feaeded867e
Author: Bryce Harrington <bryce@canonical.com>
Date:   Tue Feb 12 14:24:37 2013 -0800

    If EAGAIN returned opening drm, then try, try again.
    
    The kernel returns EAGAIN on drm open when the drm device is currently
    unavailable, such as if it is in use by another process (e.g. plymouth),
    or hasn't finished initializing (e.g. on a really fast SSD).  Check for
    this error code, and if it's hit then block until it either resolved or
    some other error returned (and in which case, log the appropriate
    messages to that effect).
    
    Signed-off-by: Bryce Harrington <bryce@canonical.com>

diff --git a/xf86drm.c b/xf86drm.c
index 2a74c80..063898f 100644
--- a/xf86drm.c
+++ b/xf86drm.c
@@ -476,6 +476,7 @@ static int drmOpenByBusid(const char *busid)
 {
     int        i, pci_domain_ok = 1;
     int        fd;
+    int        err = 0;
     const char *buf;
     drmSetVersion sv;
 
@@ -485,13 +486,19 @@ static int drmOpenByBusid(const char *busid)
 	drmMsg("drmOpenByBusid: drmOpenMinor returns %d\n", fd);
 	if (fd >= 0) {
 	    /* We need to try for 1.4 first for proper PCI domain support
-	     * and if that fails, we know the kernel is busted
+	     * and if that fails, we know either the kernel is busted or
+	     * the drm device is otherwise occupied at the moment.
 	     */
 	    sv.drm_di_major = 1;
 	    sv.drm_di_minor = 4;
 	    sv.drm_dd_major = -1;	/* Don't care */
 	    sv.drm_dd_minor = -1;	/* Don't care */
-	    if (drmSetInterfaceVersion(fd, &sv)) {
+	    err = drmSetInterfaceVersion(fd, &sv);
+	    while (err == EAGAIN) {
+	      usleep(20);               /* Just keep swimming */
+	      err = drmSetInterfaceVersion(fd, &sv);
+	    }
+	    if (err) {
 #ifndef __alpha__
 		pci_domain_ok = 0;
 #endif
@@ -499,8 +506,11 @@ static int drmOpenByBusid(const char *busid)
 		sv.drm_di_minor = 1;
 		sv.drm_dd_major = -1;       /* Don't care */
 		sv.drm_dd_minor = -1;       /* Don't care */
-		drmMsg("drmOpenByBusid: Interface 1.4 failed, trying 1.1\n",fd);
-		drmSetInterfaceVersion(fd, &sv);
+		drmMsg("drmOpenByBusid: Interface 1.4 failed (%d), trying 1.1\n", err);
+		err = drmSetInterfaceVersion(fd, &sv);
+		if (err) {
+		  drmMesg("drmOpenByBusid: Interface 1.1 failed (%d) as well\n", err);
+		}
 	    }
 	    buf = drmGetBusid(fd);
 	    drmMsg("drmOpenByBusid: drmGetBusid reports %s\n", buf);