3.0 (or SNA?) regression: failed to train DP, aborting

3.0 (or SNA?) regression: failed to train DP, aborting

[Andrew Lutomirski]

I have a Q67 (DQ67SW board) attached to a Dell U2711 via DP.  In
previous kernels, the DP link has worked flawlessly.  I just booted
3.0-final and simultaneously enabled SNA, and now when my screen goes
to sleep I don't get an image back until I power cycle the monitor.
dmesg says:

[drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting

I don't know whether this is a 3.0 regression or whether it's
triggered by SNA, but something broke.

--Andy

Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Andrew Lutomirski]

On Sat, Jul 23, 2011 at 2:40 PM, Andrew Lutomirski <luto@mit.edu> wrote:
> I have a Q67 (DQ67SW board) attached to a Dell U2711 via DP.  In
> previous kernels, the DP link has worked flawlessly.  I just booted
> 3.0-final and simultaneously enabled SNA, and now when my screen goes
> to sleep I don't get an image back until I power cycle the monitor.
> dmesg says:
>
> [drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting
>
> I don't know whether this is a 3.0 regression or whether it's
> triggered by SNA, but something broke.

It's not SNA.  Building with --disable-sna doesn't help.

>
> --Andy
>

Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Keith Packard]

[-- Attachment #1.1: Type: text/plain, Size: 1149 bytes --]

On Sat, 23 Jul 2011 14:40:36 -0400, Andrew Lutomirski <luto@mit.edu> wrote:
> I have a Q67 (DQ67SW board) attached to a Dell U2711 via DP.  In
> previous kernels, the DP link has worked flawlessly.  I just booted
> 3.0-final and simultaneously enabled SNA, and now when my screen goes
> to sleep I don't get an image back until I power cycle the monitor.
> dmesg says:
> 
> [drm:intel_dp_complete_link_train] *ERROR* failed to train DP,
> aborting

Jesse put together a set of 7 display port patches around July 7 which
were merged just after 3.0-rc6. If you try 3.0-rc6 and find that it
works, you should be able to bisect that really quickly; there are only
13 patches post-rc6 in drivers/gpu/drm/i915:

$ git bisect start v3.0 v3.0-rc6 -- drivers/gpu/drm/i915

We tested this on as many machines as we could get our hands on, but
it's a combinatorial problem between the chipset and the monitor...

> I don't know whether this is a 3.0 regression or whether it's
> triggered by SNA, but something broke.

Yeah, as you noticed, this should have no effect. Please let us know
what you find.

-- 
keith.packard@intel.com

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Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Andrew Lutomirski]

On Mon, Jul 25, 2011 at 12:54 AM, Keith Packard <keithp@keithp.com> wrote:
> On Sat, 23 Jul 2011 14:40:36 -0400, Andrew Lutomirski <luto@mit.edu> wrote:
>> I have a Q67 (DQ67SW board) attached to a Dell U2711 via DP.  In
>> previous kernels, the DP link has worked flawlessly.  I just booted
>> 3.0-final and simultaneously enabled SNA, and now when my screen goes
>> to sleep I don't get an image back until I power cycle the monitor.
>> dmesg says:
>>
>> [drm:intel_dp_complete_link_train] *ERROR* failed to train DP,
>> aborting
>
> Jesse put together a set of 7 display port patches around July 7 which
> were merged just after 3.0-rc6. If you try 3.0-rc6 and find that it
> works, you should be able to bisect that really quickly; there are only
> 13 patches post-rc6 in drivers/gpu/drm/i915:
>
> $ git bisect start v3.0 v3.0-rc6 -- drivers/gpu/drm/i915

The offending commit appears to be:

commit 885a50147f00a8a80108904bf58a18af357717f3
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Thu Jul 7 11:11:01 2011 -0700

    drm/i915/dp: remove DPMS mode tracking from DP

    We currently use this when a hot plug event is received, only checking
    the link status and re-training if we had previously configured a link.
    However if we want to preserve the DP configuration across both hot plug
    and DPMS events (which we do for userspace apps that don't respond to
    hot plug uevents), we need to unconditionally check the link and try to
    bring it up on hot plug.

    Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
    Reviewed-by: Keith Packard <keithp@keithp.com>
    Signed-off-by: Keith Packard <keithp@keithp.com>

A debugging patch and its output are attached.

If I had to guess, though, it's a race: a hotplug event happens during
the intel_dp_dpms callback, confusing the code that's trying to train
the link.

--Andy

Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Keith Packard]

[-- Attachment #1.1: Type: text/plain, Size: 437 bytes --]

On Mon, 25 Jul 2011 11:23:17 -0400, Andrew Lutomirski <luto@mit.edu> wrote:

> A debugging patch and its output are attached.

I didn't get any attachment.

> If I had to guess, though, it's a race: a hotplug event happens during
> the intel_dp_dpms callback, confusing the code that's trying to train
> the link.

Interesting possibility. Please re-send the attachments and I'll take a
look.

-- 
keith.packard@intel.com

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Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Andrew Lutomirski]

[-- Attachment #1: Type: text/plain, Size: 683 bytes --]

On Mon, Jul 25, 2011 at 12:08 PM, Keith Packard <keithp@keithp.com> wrote:
> On Mon, 25 Jul 2011 11:23:17 -0400, Andrew Lutomirski <luto@mit.edu> wrote:
>
>> A debugging patch and its output are attached.
>
> I didn't get any attachment.
>
>> If I had to guess, though, it's a race: a hotplug event happens during
>> the intel_dp_dpms callback, confusing the code that's trying to train
>> the link.
>
> Interesting possibility. Please re-send the attachments and I'll take a
> look.

Done.

I'm pretty sure the debugging patch is barking up the wrong tree.  If
you like, I can do a different one to instrument intel_dp_dpms and
hotplug later on.

>
> --
> keith.packard@intel.com
>

[-- Attachment #2: dmesg_dpms_fail.txt --]
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[  437.718439] [drm:intel_dp_link_down], 
[  439.250105] [drm:i915_hotplug_work_func], running encoder hotplug functions
[  439.250322] [drm:intel_dp_check_link_status], DPCD was 110A8401
[  439.250536] [drm:intel_dp_check_link_status], DPCD is now 110A8401
[  439.301732] [drm:intel_wait_for_vblank], vblank wait timed out
[  439.303716] [drm:intel_dp_complete_link_train], Training worked. DPCD=110A8401
[  439.303942] [drm:intel_ironlake_crt_detect_hotplug], ironlake hotplug adpa=0xf40000, result 0
[  439.303946] [drm:intel_crt_detect], CRT not detected via hotplug
[  439.303950] [drm:output_poll_execute], [CONNECTOR:5:VGA-1] status updated from 2 to 2
[  439.316359] [drm:output_poll_execute], [CONNECTOR:8:HDMI-A-1] status updated from 2 to 2
[  439.316363] [drm:ironlake_dp_detect], DPCD was 00000000
[  439.316878] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.316882] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  439.319216] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.319219] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  439.321217] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.321222] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  439.322704] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  439.322711] [drm:output_poll_execute], [CONNECTOR:11:DP-1] status updated from 2 to 2
[  439.335104] [drm:output_poll_execute], [CONNECTOR:14:HDMI-A-2] status updated from 2 to 2
[  439.347505] [drm:output_poll_execute], [CONNECTOR:16:HDMI-A-3] status updated from 2 to 2
[  439.347509] [drm:ironlake_dp_detect], DPCD was 110A8401
[  439.347724] [drm:ironlake_dp_detect], Try 0: ret=4 DPCD=110A8401
[  439.347730] [drm:ironlake_dp_detect], Happy now!
[  439.347732] [drm:ironlake_dp_detect], No link. DPCD: 110a8401
[  439.348687] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  439.376262] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  439.403831] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  439.403835] [drm:drm_detect_monitor_audio], Monitor has basic audio support
[  439.403838] [drm:output_poll_execute], [CONNECTOR:17:DP-2] status updated from 1 to 1
[  439.403842] [drm:ironlake_dp_detect], DPCD was 00000000
[  439.404357] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.404360] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  439.406164] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.406165] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  439.408167] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  439.408169] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  439.409663] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  439.409671] [drm:output_poll_execute], [CONNECTOR:19:DP-3] status updated from 2 to 2
[  442.956501] [drm:ironlake_crtc_dpms], crtc 0/0 dpms on
[  443.120115] [drm:intel_dp_link_down], 
[  443.137460] [drm:ironlake_crtc_dpms], crtc 0/0 dpms off
[  443.189440] [drm:intel_wait_for_vblank], vblank wait timed out
[  443.211838] [drm:sandybridge_update_wm], FIFO watermarks For pipe A - plane 13, cursor: 6
[  443.211845] [drm:ironlake_check_srwm], watermark 1: display plane 25, fbc lines 3, cursor 6
[  443.211849] [drm:ironlake_check_srwm], watermark 2: display plane 33, fbc lines 3, cursor 6
[  443.211854] [drm:ironlake_check_srwm], watermark 3: display plane 169, fbc lines 4, cursor 10
[  443.211858] [drm:intel_update_fbc], 
[  444.644607] [drm:i915_hotplug_work_func], running encoder hotplug functions
[  444.644823] [drm:intel_dp_check_link_status], DPCD was 110A8401
[  444.645037] [drm:intel_dp_check_link_status], DPCD is now 110A8401
[  444.696526] [drm:intel_wait_for_vblank], vblank wait timed out
[  444.751506] [drm:intel_wait_for_vblank], vblank wait timed out
[  444.806485] [drm:intel_wait_for_vblank], vblank wait timed out
[  444.861428] [drm:intel_wait_for_vblank], vblank wait timed out
[  444.916419] [drm:intel_wait_for_vblank], vblank wait timed out
[  444.971376] [drm:intel_wait_for_vblank], vblank wait timed out
[  445.026356] [drm:intel_wait_for_vblank], vblank wait timed out
[  445.028771] [drm:intel_dp_complete_link_train] *ERROR* failed to train DP, aborting
[  445.028775] [drm:intel_dp_complete_link_train], DPCD is 110A8401
[  445.028780] [drm:intel_dp_link_down], 
[  445.046329] [drm:intel_dp_complete_link_train], Training worked. DPCD=110A8401
[  445.046552] [drm:intel_ironlake_crt_detect_hotplug], ironlake hotplug adpa=0xf40000, result 0
[  445.046556] [drm:intel_crt_detect], CRT not detected via hotplug
[  445.046560] [drm:output_poll_execute], [CONNECTOR:5:VGA-1] status updated from 2 to 2
[  445.059011] [drm:output_poll_execute], [CONNECTOR:8:HDMI-A-1] status updated from 2 to 2
[  445.059015] [drm:ironlake_dp_detect], DPCD was 00000000
[  445.059531] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.059535] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  445.061820] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.061821] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  445.063822] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.063824] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  445.065312] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  445.065318] [drm:output_poll_execute], [CONNECTOR:11:DP-1] status updated from 2 to 2
[  445.077692] [drm:output_poll_execute], [CONNECTOR:14:HDMI-A-2] status updated from 2 to 2
[  445.090041] [drm:output_poll_execute], [CONNECTOR:16:HDMI-A-3] status updated from 2 to 2
[  445.090043] [drm:ironlake_dp_detect], DPCD was 110A8401
[  445.090254] [drm:ironlake_dp_detect], Try 0: ret=4 DPCD=110A8401
[  445.090256] [drm:ironlake_dp_detect], Happy now!
[  445.090257] [drm:ironlake_dp_detect], No link. DPCD: 110a8401
[  445.091304] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  445.118864] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  445.146423] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  445.146424] [drm:drm_detect_monitor_audio], Monitor has basic audio support
[  445.146426] [drm:output_poll_execute], [CONNECTOR:17:DP-2] status updated from 1 to 1
[  445.146428] [drm:ironlake_dp_detect], DPCD was 00000000
[  445.146941] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.146942] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  445.148769] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.148770] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  445.150771] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  445.150773] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  445.152259] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  445.152265] [drm:output_poll_execute], [CONNECTOR:19:DP-3] status updated from 2 to 2
[  453.112596] [drm:ironlake_crtc_dpms], crtc 0/0 dpms on
[  453.112602] [drm:sandybridge_update_wm], FIFO watermarks For pipe A - plane 13, cursor: 6
[  453.112607] [drm:ironlake_check_srwm], watermark 1: display plane 25, fbc lines 3, cursor 6
[  453.112611] [drm:ironlake_check_srwm], watermark 2: display plane 33, fbc lines 3, cursor 6
[  453.112616] [drm:ironlake_check_srwm], watermark 3: display plane 169, fbc lines 4, cursor 10
[  453.164539] [drm:intel_wait_for_vblank], vblank wait timed out
[  453.216511] [drm:intel_wait_for_vblank], vblank wait timed out
[  453.217324] [drm:gen6_fdi_link_train], FDI_RX_IIR 0x100
[  453.217329] [drm:gen6_fdi_link_train], FDI train 1 done.
[  453.217989] [drm:gen6_fdi_link_train], FDI_RX_IIR 0x600
[  453.217994] [drm:gen6_fdi_link_train], FDI train 2 done.
[  453.217996] [drm:gen6_fdi_link_train], FDI train done.
[  453.219256] [drm:intel_update_fbc], 
[  468.967065] usb 3-1: USB disconnect, device number 2
[  468.967069] usb 3-1.1: USB disconnect, device number 3
[  468.967072] usb 3-1.1.1: USB disconnect, device number 4
[  470.871840] [drm:i915_hotplug_work_func], running encoder hotplug functions
[  470.872364] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5013003e
[  470.874264] [drm:intel_dp_check_link_status], DPCD was 110A8401
[  470.874479] [drm:intel_dp_check_link_status], DPCD is now 110A8401
[  470.926022] [drm:intel_wait_for_vblank], vblank wait timed out
[  470.928002] [drm:intel_dp_complete_link_train], Training worked. DPCD=110A8401
[  470.928233] [drm:intel_ironlake_crt_detect_hotplug], ironlake hotplug adpa=0xf40000, result 0
[  470.928238] [drm:intel_crt_detect], CRT not detected via hotplug
[  470.928241] [drm:output_poll_execute], [CONNECTOR:5:VGA-1] status updated from 2 to 2
[  470.940644] [drm:output_poll_execute], [CONNECTOR:8:HDMI-A-1] status updated from 2 to 2
[  470.940648] [drm:ironlake_dp_detect], DPCD was 00000000
[  470.941164] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  470.941168] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  470.943524] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  470.943528] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  470.945523] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  470.945526] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  470.947009] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  470.947013] [drm:output_poll_execute], [CONNECTOR:11:DP-1] status updated from 2 to 2
[  470.959413] [drm:output_poll_execute], [CONNECTOR:14:HDMI-A-2] status updated from 2 to 2
[  470.971802] [drm:output_poll_execute], [CONNECTOR:16:HDMI-A-3] status updated from 2 to 2
[  470.971806] [drm:ironlake_dp_detect], DPCD was 110A8401
[  470.972020] [drm:ironlake_dp_detect], Try 0: ret=4 DPCD=110A8401
[  470.972026] [drm:ironlake_dp_detect], Happy now!
[  470.972029] [drm:ironlake_dp_detect], No link. DPCD: 110a8401
[  470.973080] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  471.000644] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  471.028210] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  471.028214] [drm:drm_detect_monitor_audio], Monitor has basic audio support
[  471.028218] [drm:output_poll_execute], [CONNECTOR:17:DP-2] status updated from 1 to 1
[  471.028222] [drm:ironlake_dp_detect], DPCD was 00000000
[  471.028736] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  471.028739] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  471.030473] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  471.030476] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  471.032471] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  471.032474] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  471.033958] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  471.033962] [drm:output_poll_execute], [CONNECTOR:19:DP-3] status updated from 2 to 2
[  473.703741] [drm:i915_hotplug_work_func], running encoder hotplug functions
[  473.703958] [drm:intel_dp_check_link_status], DPCD was 110A8401
[  473.704172] [drm:intel_dp_check_link_status], DPCD is now 110A8401
[  473.704183] [drm:intel_ironlake_crt_detect_hotplug], ironlake hotplug adpa=0xf40000, result 0
[  473.704187] [drm:intel_crt_detect], CRT not detected via hotplug
[  473.704190] [drm:output_poll_execute], [CONNECTOR:5:VGA-1] status updated from 2 to 2
[  473.716606] [drm:output_poll_execute], [CONNECTOR:8:HDMI-A-1] status updated from 2 to 2
[  473.716611] [drm:ironlake_dp_detect], DPCD was 00000000
[  473.717126] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.717129] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  473.718885] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.718889] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  473.720887] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.720892] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  473.722377] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  473.722383] [drm:output_poll_execute], [CONNECTOR:11:DP-1] status updated from 2 to 2
[  473.734786] [drm:output_poll_execute], [CONNECTOR:14:HDMI-A-2] status updated from 2 to 2
[  473.747175] [drm:output_poll_execute], [CONNECTOR:16:HDMI-A-3] status updated from 2 to 2
[  473.747179] [drm:ironlake_dp_detect], DPCD was 110A8401
[  473.747394] [drm:ironlake_dp_detect], Try 0: ret=4 DPCD=110A8401
[  473.747399] [drm:ironlake_dp_detect], Happy now!
[  473.747402] [drm:ironlake_dp_detect], No link. DPCD: 110a8401
[  473.748458] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  473.776037] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  473.803604] [drm:i2c_algo_dp_aux_xfer], dp_aux_xfer return 2
[  473.803608] [drm:drm_detect_monitor_audio], Monitor has basic audio support
[  473.803611] [drm:output_poll_execute], [CONNECTOR:17:DP-2] status updated from 1 to 1
[  473.803615] [drm:ironlake_dp_detect], DPCD was 00000000
[  473.804130] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.804133] [drm:ironlake_dp_detect], Try 0: ret=-110 DPCD=00000000
[  473.805832] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.805833] [drm:ironlake_dp_detect], Try 1: ret=-110 DPCD=00000000
[  473.807836] [drm:intel_dp_aux_ch], dp_aux_ch timeout status 0x5143003e
[  473.807838] [drm:ironlake_dp_detect], Try 2: ret=-110 DPCD=00000000
[  473.809327] [drm:ironlake_dp_detect], No link. DPCD: 00000000
[  473.809333] [drm:output_poll_execute], [CONNECTOR:19:DP-3] status updated from 2 to 2

[-- Attachment #3: i915-debugging-hack.patch --]
[-- Type: text/x-patch, Size: 2747 bytes --]

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 5f97c17..501b94d 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1375,6 +1375,9 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 
 		if (cr_tries > 5) {
 			DRM_ERROR("failed to train DP, aborting\n");
+			DRM_DEBUG_KMS("DPCD is %02hX%02hX%02hX%02hX\n",
+				      intel_dp->dpcd[0], intel_dp->dpcd[1],
+				      intel_dp->dpcd[2], intel_dp->dpcd[3]);
 			intel_dp_link_down(intel_dp);
 			break;
 		}
@@ -1427,6 +1430,10 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 		++tries;
 	}
 
+	DRM_DEBUG_KMS("Training worked. DPCD=%02hX%02hX%02hX%02hX\n",
+		      intel_dp->dpcd[0], intel_dp->dpcd[1],
+		      intel_dp->dpcd[2], intel_dp->dpcd[3]);
+
 	if (HAS_PCH_CPT(dev) && !is_edp(intel_dp))
 		reg = DP | DP_LINK_TRAIN_OFF_CPT;
 	else
@@ -1530,15 +1537,24 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 		return;
 	}
 
+	DRM_DEBUG_KMS("DPCD was %02hX%02hX%02hX%02hX\n",
+		      intel_dp->dpcd[0], intel_dp->dpcd[1],
+		      intel_dp->dpcd[2], intel_dp->dpcd[3]);
+
 	/* Try to read receiver status if the link appears to be up */
 	ret = intel_dp_aux_native_read(intel_dp,
 				       0x000, intel_dp->dpcd,
 				       sizeof (intel_dp->dpcd));
 	if (ret != sizeof(intel_dp->dpcd)) {
+		DRM_DEBUG_KMS("Failed to read DPCD\n");
 		intel_dp_link_down(intel_dp);
 		return;
 	}
 
+	DRM_DEBUG_KMS("DPCD is now %02hX%02hX%02hX%02hX\n",
+		      intel_dp->dpcd[0], intel_dp->dpcd[1],
+		      intel_dp->dpcd[2], intel_dp->dpcd[3]);
+
 	if (!intel_channel_eq_ok(intel_dp)) {
 		intel_dp_start_link_train(intel_dp);
 		intel_dp_complete_link_train(intel_dp);
@@ -1559,19 +1575,29 @@ ironlake_dp_detect(struct intel_dp *intel_dp)
 		return status;
 	}
 
+	DRM_DEBUG_KMS("DPCD was %02hX%02hX%02hX%02hX\n",
+		      intel_dp->dpcd[0], intel_dp->dpcd[1],
+		      intel_dp->dpcd[2], intel_dp->dpcd[3]);
+
 	status = connector_status_disconnected;
 	for (i = 0; i < 3; i++) {
 		ret = intel_dp_aux_native_read(intel_dp,
 					       0x000, intel_dp->dpcd,
 					       sizeof (intel_dp->dpcd));
+		DRM_DEBUG_KMS("Try %d: ret=%d DPCD=%02hX%02hX%02hX%02hX\n",
+			      i,
+			      ret,
+			      intel_dp->dpcd[0], intel_dp->dpcd[1],
+			      intel_dp->dpcd[2], intel_dp->dpcd[3]);
 		if (ret == sizeof(intel_dp->dpcd) &&
 		    intel_dp->dpcd[DP_DPCD_REV] != 0) {
+			DRM_DEBUG_KMS("Happy now!");
 			status = connector_status_connected;
 			break;
 		}
 		msleep(1);
 	}
-	DRM_DEBUG_KMS("DPCD: %hx%hx%hx%hx\n", intel_dp->dpcd[0],
+	DRM_DEBUG_KMS("No link. DPCD: %02hx%02hx%02hx%02hx\n", intel_dp->dpcd[0],
 		      intel_dp->dpcd[1], intel_dp->dpcd[2], intel_dp->dpcd[3]);
 	return status;
 }

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Re: 3.0 (or SNA?) regression: failed to train DP, aborting

[Keith Packard]

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On Mon, 25 Jul 2011 13:15:54 -0400, Andrew Lutomirski <luto@mit.edu> wrote:

> Done.

Jesse Barnes and I discovered, much to our horror, that the hotplugging
path isn't holding the struct mutex while attempting to retrain the DP
link. That means that an application could well be doing a bit of
overlapping modesetting fun. And, it seems like the trace you provided
shows precisely that happening.

Care to try this patch? It's fixed my persistent hot-unplug problems.

From bba6ccca57f0536fb5aae278527939d7247a1f53 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Mon, 25 Jul 2011 10:04:56 -0700
Subject: [PATCH] drm/i915: Hold struct_mutex during hotplug processing

Hotplug detection is a mode setting operation and must hold the
struct_mutex or risk colliding with other mode setting operations.

In particular, the display port hotplug function attempts to re-train
the link if the monitor is supposed to be running when plugged back
in. If that happens while mode setting is underway, the link will get
scrambled, leaving it in an inconsistent state.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 drivers/gpu/drm/i915/i915_irq.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 3b03f85..5fe8f28 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -306,12 +306,15 @@ static void i915_hotplug_work_func(struct work_struct *work)
 	struct drm_mode_config *mode_config = &dev->mode_config;
 	struct intel_encoder *encoder;
 
+	mutex_lock(&dev_priv->dev->struct_mutex);
 	DRM_DEBUG_KMS("running encoder hotplug functions\n");
 
 	list_for_each_entry(encoder, &mode_config->encoder_list, base.head)
 		if (encoder->hot_plug)
 			encoder->hot_plug(encoder);
 
+	mutex_unlock(&dev_priv->dev->struct_mutex);
+
 	/* Just fire off a uevent and let userspace tell us what to do */
 	drm_helper_hpd_irq_event(dev);
 }
-- 
1.7.5.4



-- 
keith.packard@intel.com

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