Re: [git pull] drm for 4.4-rc1

From: Stefan Lippers-Hollmann
Date: Wed Dec 09 2015 - 22:04:40 EST

Hi

On 2015-11-09, Dave Airlie wrote:
[...]
The following changes since commit 06d1ee32a4d25356a710b49d5e95dbdd68bdf505:

Merge branch 'drm-fixes' of git://people.freedesktop.org/~airlied/linux (2015-10-13 09:45:21 -0700)

are available in the git repository at:

git://people.freedesktop.org/~airlied/linux drm-next

for you to fetch changes up to 816d2206f0f9953ca854e4ff1a2749a5cbd62715:

Merge tag 'drm-intel-next-fixes-2015-11-06' of git://anongit.freedesktop.org/drm-intel into drm-next (2015-11-07 17:16:59 +1000)
[...]
> drm/i915: Check live status before reading edid
[...]

This patch seems to introduce a regression for i915 in Linus'
v4.4-rc4-60-g9a0f76f, relative to v4.3 (and 4.3.1), on a sandy-bridge
(Intel DH67CL) system with a single HDMI connected monitor (Medion MD20094)
attached. Immediately after the modeswitch, the monitor switches off and
stays off. Nothing catches my eyes in dmesg or Xorg.0.log, but bisecting
the issue points me at:

237ed86c693d8a8e4db476976aeb30df4deac74b is the first bad commit
commit 237ed86c693d8a8e4db476976aeb30df4deac74b
Author: Sonika Jindal <sonika.jindal@xxxxxxxxx>
Date: Tue Sep 15 09:44:20 2015 +0530

drm/i915: Check live status before reading edid

The Bspec is very clear that Live status must be checked about before
trying to read EDID over DDC channel. This patch makes sure that HDMI
EDID is read only when live status is up.

The live status doesn't seem to perform very consistent across various
platforms when tested with different monitors. The reason behind that is
some monitors are late to provide right voltage to set live_status up.
So, after getting the interrupt, for a small duration, live status reg
fluctuates, and then settles down showing the correct staus.

This is explained here in, in a rough way:
HPD line ________________
|\ T1 = Monitor Hotplug causing IRQ
| \______________________________________
| |
| |
| | T2 = Live status is stable
| | _____________________________________
| | /|
Live status _____________|_|/ |
| | |
| | |
| | |
T0 T1 T2

(Between T1 and T2 Live status fluctuates or can be even low, depending on
the monitor)

After several experiments, we have concluded that a max delay
of 30ms is enough to allow the live status to settle down with
most of the monitors. This total delay of 30ms has been split into
a resolution of 3 retries of 10ms each, for the better cases.

This delay is kept at 30ms, keeping in consideration that, HDCP compliance
expect the HPD handler to respond a plug out in 100ms, by disabling port.

v2: Adding checks for VLV/CHV as well. Reusing old ibx and g4x functions
to check digital port status. Adding a separate function to get bxt live
status (Daniel)
v3: Using intel_encoder->hpd_pin to check the live status (Siva)
Moving the live status read to intel_hdmi_probe and passing parameter
to read/not to read the edid. (me)
v4:
* Added live status check for all platforms using
intel_digital_port_connected.
* Rebased on top of Jani's DP cleanup series
* Some monitors take time in setting the live status. So retry for few
times if this is a connect HPD
v5: Removed extra "drm/i915" from commit message. Adding Shashank's sob
which was missed.
v6: Drop the (!detect_edid && !live_status check) check because for DDI
ports which are enumerated as hdmi as well as DP, we don't have a
mechanism to differentiate between DP and hdmi inside the encoder's
hot_plug. This leads to call to the hdmi's hot_plug hook for DP as well
as hdmi which leads to issues during unplug because of the above check.
v7: Make intel_digital_port_connected global in this patch, some
reformatting of while loop, adding a print when live status is not
up. (Rodrigo)
v8: Rebase it on nightly which involved skipping the hot_plug hook for now
and letting the live_status check happen in detect until the hpd handling
part is finalized (Daniel)

Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxxxx>
Signed-off-by: Sonika Jindal <sonika.jindal@xxxxxxxxx>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>

:040000 040000 85f19ff45ffe39cee99a7a9b0e9dadf9fe71553f 0094b6c634580a496c5cdbf77f13fe5fa769c3e3 M drivers

$ git bisect log
# bad: [9a0f76fde9ad2c00c0cf13aaf3dfb9d886dc578c] Merge tag 'for-linus-4.4-1' of git://git.code.sf.net/p/openipmi/linux-ipmi
# good: [6a13feb9c82803e2b815eca72fa7a9f5561d7861] Linux 4.3
git bisect start 'HEAD' 'v4.3'
# good: [8e483ed1342a4ea45b70f0f33ac54eff7a33d918] Merge tag 'char-misc-4.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc
git bisect good 8e483ed1342a4ea45b70f0f33ac54eff7a33d918
# bad: [3e82806b97398d542a5e03bd94861f79ce10ecee] Merge branch 'drm-next' of git://people.freedesktop.org/~airlied/linux
git bisect bad 3e82806b97398d542a5e03bd94861f79ce10ecee
# good: [0280d1a099da1d211e76ec47cc0944c993a36316] Merge tag 'sound-4.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound
git bisect good 0280d1a099da1d211e76ec47cc0944c993a36316
# good: [123a28d8b522b03dd97c1f791245924088616ac0] Merge branch 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs
git bisect good 123a28d8b522b03dd97c1f791245924088616ac0
# bad: [b10f1b20171945b49988b2b1fe68cb312cc36d32] drm/i915/skl: Prevent unclaimed register writes on skylake.
git bisect bad b10f1b20171945b49988b2b1fe68cb312cc36d32
# bad: [89e3e1427629027dc33e576fc002880a02a7e50c] drm/i915: Support NV12 in rotated GGTT mapping
git bisect bad 89e3e1427629027dc33e576fc002880a02a7e50c
# good: [0b2eb33e5e2b4aaeaa786d551a1b5f08904a9bfc] drm/i915: LPT:LP needs port A HPD enabled in both north and south
git bisect good 0b2eb33e5e2b4aaeaa786d551a1b5f08904a9bfc
# good: [eb120ef6a3e18780e7464e7de70221d06dfe5845] drm/i915: add more debug info for when atomic updates fail v3
git bisect good eb120ef6a3e18780e7464e7de70221d06dfe5845
# bad: [7aefe2b50a0be5c85e7702bff110e5e187fbe4b5] drm/i915: Fix fastboot scalers for skylake.
git bisect bad 7aefe2b50a0be5c85e7702bff110e5e187fbe4b5
# good: [83e3337204b2385d20e149c8fe91bb2719978df2] drm/i915: Increase maximum polling time to 50ms for forcewake request/clear ack
git bisect good 83e3337204b2385d20e149c8fe91bb2719978df2
# bad: [9eca6832f7254d49d25494da7d47c0f8a24f7862] drm/i915: Move scanline_offset and timestamping constant setup to intel_modeset_readout_hw_state()
git bisect bad 9eca6832f7254d49d25494da7d47c0f8a24f7862
# good: [d2e08c0f34438af791482de8abf2c8e4e573b1d3] drm/i915/bxt: DSI prepare changes for BXT
git bisect good d2e08c0f34438af791482de8abf2c8e4e573b1d3
# bad: [7f4c62840cc416986f983a8c68f7010c97e06daf] drm/i915: Assign hwmode after encoder state readout
git bisect bad 7f4c62840cc416986f983a8c68f7010c97e06daf
# bad: [237ed86c693d8a8e4db476976aeb30df4deac74b] drm/i915: Check live status before reading edid
git bisect bad 237ed86c693d8a8e4db476976aeb30df4deac74b
# first bad commit: [237ed86c693d8a8e4db476976aeb30df4deac74b] drm/i915: Check live status before reading edid

Unfortunately reverting only this patch on top of v4.4-rc4-60-g9a0f76f
doesn't appear to be quite straight forward. What is the best approach
to debug this further?

The very same kernel works fine on two ivy-bridge systems (different
monitors, one connected via HDMI, one via DVI) and an Atom N270 based
system (Intel D945GSEJT, monitor connected via DVI).

Regards
Stefan Lippers-Hollmann
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