Commit
commit 2a59eadf8165bd70780ac16220456c6196ac3ff1
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sun Jul 7 09:13:49 2013 +0100

    sna/gen4: Remove the glyph mask hack and tune the flush w/a
    
    Remove the hack from the glyph path to force the use of an auxiliary
    channel, and reduce the maximum amount of inflight vertices until we can
    then render glyphs with no corruption (at least in my test case).
    
    Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

reverts
--- a/src/sna/sna_glyphs.c
+++ b/src/sna/sna_glyphs.c
@@ -1287,7 +1287,7 @@ next_image:
                                             __FUNCTION__,
                                             (int)p->atlas->format,
                                             (int)(format->depth << 24 | format->format)));
-                                       if (p->atlas->format == (format->depth << 24 | format->format)) {
+                                       if (p->atlas->format == (format->depth << 24 | format->format) && (sna->kgem.gen >> 3) != 4) /* XXX cache corruption? 
how? */ {
                                                ok = sna->render.composite(sna, PictOpAdd,
                                                                           p->atlas, NULL, mask,
                                                                           0, 0, 0, 0, 0, 0,


and fonts corruption is back on my
00:02.0 VGA compatible controller: Intel Corporation Mobile 4 Series Chipset Integrated Graphics Controller (rev 07) (prog-if 00 [VGA controller])
(thinkpad t400)

Reverting chunk above and fonts corruption is gone.

kde4.11 + xserver1.14.4 + kernel 3.12 here.