[Intel-gfx] Intel-gfx related suspend-to-ram issues on IBM R31

[Thomas Richter]

Hi Daniel, hi Ville,

thanks for integrating my patches of the DVO chip of my old IBM R31.
With this patch in place, dithering on the laptop works now.

However, I recently upgraded to Debian Stretch, and since then, I'm
having either issues with 3D acceleration or with suspend-to-RAM.

Details are as follows: The machine comes with the infamous i830M
chipset, to be precise:

00:00.0 Host bridge: Intel Corporation 82830M/MG/MP Host Bridge (rev 04)
00:02.0 VGA compatible controller: Intel Corporation 82830M/MG
Integrated Graphics Controller (rev 04)
00:02.1 Display controller: Intel Corporation 82830M/MG Integrated
Graphics Controller

I previously run the machine on a 4.1.38 kernel and Debian jessie, and
everything (almost) worked. 3D acceleration worked (stable), and
suspend-to-ram and suspend-to-disk worked. I had to disable the S3 state
by a custom dsdt, but except that, everything was ok.

Now, after upgrading to stretch, something must have changed in the
userland. Even after booting with the identical 4.1.38 kernel, 3D
acceleration broke.

*Q1: What changed in userland, and is there a way to revert the changes?*

I tried now the system with various other kernels. Here is what happens:

- Under 4.9.49 (longterm), 3D acceleration works, the machine enters the
S1 state, but does not wake up anymore. Trying a suspend-trace, the
machine claims to hang in power/main.c:

[    0.952198]   Magic number: 0:791:321
[    0.967849]   hash matches drivers/base/power/main.c:742

This is the same location the machine hangs at when allowing it to enter
S3 (and there does not wake up). A code analysis is inconclusive.

- linux-4.1.38: (The old kernel): With new userland, 3D acceleration
does not work at all. S1 standby and resume work. With old userland, 3D
acceleration works before and after resume to S1 state (no issues).

- linux-4.1.44: 3d acceleration with new userland hangs, then stops
working with a GPU lockup, S1 works as in 4.1.38.

- linux-4.2.8: 3d acceleration with new userland unstable, breaks down
sooner or later, S1 standby and resume works, but GPU hangs after wakeup
and is then disabled.

- linux-4.3.6:  3d acceleration works, suspend to ram does not work at
all, i.e. the system does not even enter the S1 state.

- linux-4.14.0-rc1 (the latest release candidate on www.kernel.org): 3d
acceleration works, suspend does not work at all, the machine does not
enter the S1 state.

- linux 4.13.5-rc5+ (intel-drm, head branch): quite the same (machine
does not enter S1 state)

- linux 4.14.0-rc1+ (intel-drm-nightly): quite the same (machine does
not enter S1 state).

Enter S1 state: The IBM R31 has a status LED (a moon) that is lit
whenever the machine is in S1 or S3 state.

Any other hints or pointers I should try - or to help you debugging? It
is quite unsatisfying that the machine worked perfectly with jessie, but
3D broke with the latest userland.

Greetings,
	Thomas