[Intel-gfx] debugging Haswell eDP black screen after S3

[Ben Guthro]

I am attempting to debug an issue with some Haswell laptop systems
which do not restore their screen after resuming from S3 when running
on the stable 3.8 kernel (3.8.13)
The backlight is OK, but the screen is just black.

In trying to determine what was going wrong, I tried looking at the
output of intel_reg_dumper, in a good, and bad case:

diff -u good_reg.txt bad_reg.txt
--- good_reg.txt	2013-05-14 15:08:44.361997000 +0000
+++ bad_reg.txt	2013-05-14 15:09:20.480000000 +0000
@@ -1,5 +1,4 @@
-                 DCC: 0x00000000 (0x00000000f3400000
0x00000000f37fffff 0x00000000��
-�)
+                 DCC: 0x00000000 (0x00000000f3400000
0x00000000f37fffff 0x00000000��=�)
            CHDECMISC: 0x00000000 (none, ch2 enh disabled, ch1 enh
disabled, ch0 enh disabled, flex disabled, ep not present)
               C0DRB0: 0x00000000 (0x0000)
               C0DRB1: 0x00000000 (0x0000)
@@ -63,17 +62,17 @@
      PIPEA_DP_LINK_N: 0x00000000
        CURSOR_A_BASE: 0x01061000
     CURSOR_A_CONTROL: 0x04000027
-   CURSOR_A_POSITION: 0x03a3032f
+   CURSOR_A_POSITION: 0x01bb03fb
                 FPA0: 0x00000000 (n = 0, m1 = 0, m2 = 0)
                 FPA1: 0x00000000 (n = 0, m1 = 0, m2 = 0)
               DPLL_A: 0x00000000 (disabled, non-dvo, VGA, default
clock, unknown mode, p1 = 0, p2 = 0)
            DPLL_A_MD: 0x00000000
-            HTOTAL_A: 0x0821077f (1920 active, 2082 total)
-            HBLANK_A: 0x0821077f (1920 start, 2082 end)
-             HSYNC_A: 0x081307af (1968 start, 2068 end)
-            VTOTAL_A: 0x045f0437 (1080 active, 1120 total)
-            VBLANK_A: 0x045f0437 (1080 start, 1120 end)
-             VSYNC_A: 0x044b0441 (1090 start, 1100 end)
+            HTOTAL_A: 0x00000000 (1 active, 1 total)
+            HBLANK_A: 0x00000000 (1 start, 1 end)
+             HSYNC_A: 0x00000000 (1 start, 1 end)
+            VTOTAL_A: 0x00000000 (1 active, 1 total)
+            VBLANK_A: 0x00000000 (1 start, 1 end)
+             VSYNC_A: 0x00000000 (1 start, 1 end)
            BCLRPAT_A: 0x00000000
         VSYNCSHIFT_A: 0x00000000
             DSPBCNTR: 0x00004000 (disabled, pipe A)


It appears the registers that are saved, and restored in
i915_save_modeset_reg / i915_restore_modeset_reg is not working
properly.

When I put some debug in, I discovered that it was bailing out of
i915_save_modeset_reg early since the DRIVER_MODESET bit was cleared.
However, it was set at the end of i915_init()
This, of course, confuses me.

Am I seeing memory corruption here?


Any insight is appreciated.

Ben