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

[Ben Guthro]

On Tue, May 14, 2013 at 5:01 PM, Ben Guthro <ben at guthro.net> wrote:
> 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?

It looks like I misread the code here, inversing an if statement state.

That said, I don't really have any clues as to why the display is
black after resuming from S3

Is this an eDP training issue? Are there any changesets I can try backporting?
I tried this, but it didn't seem to help:
https://patchwork.kernel.org/patch/2516601/