Bug 23894

System Environment:
--------------------------
Platform:       945GM
Libdrm:		(master)67e4172394a88d4922fb8d9c7c3d96ce7e02c5a6
Mesa:		(master)57d16c4cc37689710f951cb13981e2efc160cd23
Xserver:		(master)8fb3fa28a5a1b36cdaad38055a607400828b9e1c
Xf86_video_intel:		(master)efbcf29dd1a1ca058b7a2a93f0685102c06c9369
Kernel:       (drm-intel-next)7e61615857c6fb3afbcb43f5c4e97511a923f5a8


Bug detailed description:
-------------------------
This issue happens on 945GM and 945G, but seems not happening with mesa_7_6_branch on another 945GME.
Some piglit tests (general/read-front, general/texgen, shaders/fp-kil, shaders/fp-lit-mask, shaders/trinity-fp1, shaders/fp-incomplete-tex, shaders/fp-fragment-position, mesa/crossbar, texturing/texrect-many) will segement falut due to following commit:
Author: Eric Anholt <eric@anholt.net>
Date:   Thu Sep 10 09:26:38 2009 -0700

    intel: Don't forget to map the depth read buffer in spans.

    This broke BlitFramebufferEXT(GL_DEPTH_BUFFER_BIT).


./read-front
(gdb) bt
#0  0x00000000 in ?? ()
#1  0xb7bb60ff in _swrast_read_rgba_span (ctx=0x90838a0, rb=0x93c0b78, n=1, x=0, y=0,
    dstType=5126, rgba=0xb77fe008) at swrast/s_span.c:1583
#2  0xb7bb4c28 in _swrast_ReadPixels (ctx=0x90838a0, x=0, y=0, width=1, height=1, format=6407,
    type=5126, packing=0x90907c4, pixels=0xbfcf3254) at swrast/s_readpix.c:422
#3  0xb7a907ce in intelReadPixels (ctx=0x90838a0, x=0, y=0, width=1, height=1, format=6407,
    type=5126, pack=0x90907c4, pixels=0xbfcf3254) at intel_pixel_read.c:314
#4  0xb7b30dd3 in _mesa_ReadPixels (x=0, y=0, width=1, height=1, format=6407, type=5126,
    pixels=0xbfcf3254) at main/readpix.c:208
#5  0x08049c2d in piglit_probe_pixel_rgb ()
#6  0x080497c4 in display ()
#7  0xb7eb54e2 in processWindowWorkList (window=0x9070d60) at glut_event.c:1306
#8  0xb7eb6138 in glutMainLoop () at glut_event.c:1356
#9  0x080499a7 in main ()