[Bug 48772] New: Signal unstable over Display Port on 2560x1440 monitor

[Bug 48772] New: Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

             Bug #: 48772
           Summary: Signal unstable over Display Port on 2560x1440 monitor
    Classification: Unclassified
           Product: DRI
           Version: XOrg CVS
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Radeon
        AssignedTo: dri-devel@lists.freedesktop.org
        ReportedBy: tvrtko.ursulin@onelan.co.uk


AMD G-T56N (Radeon HD 6310) hardware with kernel 3.4-rc3 with a Xorg DDX from
28.03.2012. plus a tiling patch from bug 47765.

Dell U2711 monitor native resolution is 2560x1440 on which Display Port
connection is unstable.

I get periodic very brief flashes of vertical noise areas, full screen width,
at various vertical positions, but possible always at least roughly the same
height. Then the screen goes black for a second, comes back for a while,
flashing, or straight back to black and so on. Timings do not look regular,
although I haven't actually timed and analysed them.

Bringing the resolution down to 1920x1200 and it works fine.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

--- Comment #1 from Alex Deucher <agd5f@yahoo.com> 2012-04-16 08:13:28 UTC ---
Sounds like display bandwidth/watermark issues.  Does booting with
radeon.disp_priority=2 on the kernel command line in grub help?  Also does
disabling tiling help?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #2 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-16 08:30:32 PDT ---
radeon.disp_priority=2 seems to have no effect. Perhaps it decreased the
frequency between screen blackouts, but my sample size is small and randomness
of the timings makes me uneasy to claim so yet. Would it make sense for it to
have such effect?

Is testing with tiling disabled relevant given the problem happens also without
X running?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

--- Comment #3 from Alex Deucher <agd5f@yahoo.com> 2012-04-16 08:43:47 PDT ---
(In reply to comment #2)
> radeon.disp_priority=2 seems to have no effect. Perhaps it decreased the
> frequency between screen blackouts, but my sample size is small and randomness
> of the timings makes me uneasy to claim so yet. Would it make sense for it to
> have such effect?
> 

Sure.  Setting that option sets the display priority in the memory controller
to the highest possible level. If the MC is still having problems keeping up,
it may be that your system can't handle a monitor that big.

Alternatively, your monitor may not like the set of pll dividers selected by
the driver in this case or spread spectrum settings.  You might try setting the
RADEON_PLL_PREFER_MINM_OVER_MAXP or RADEON_PLL_USE_FRAC_FB_DIV pll flags in
atombios_adjust_pll().

What link speed and number of lanes are being used for that mode?  Does the
monitor support downspread?

Does the proprietary driver work ok with that monitor?

> Is testing with tiling disabled relevant given the problem happens also without
> X running?

That should be equivalent.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

--- Comment #4 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-16 08:49:59 PDT ---
(In reply to comment #3)
> (In reply to comment #2)
> > radeon.disp_priority=2 seems to have no effect. Perhaps it decreased the
> > frequency between screen blackouts, but my sample size is small and randomness
> > of the timings makes me uneasy to claim so yet. Would it make sense for it to
> > have such effect?
> > 
> 
> Sure.  Setting that option sets the display priority in the memory controller
> to the highest possible level. If the MC is still having problems keeping up,
> it may be that your system can't handle a monitor that big.
> 
> Alternatively, your monitor may not like the set of pll dividers selected by
> the driver in this case or spread spectrum settings.  You might try setting the
> RADEON_PLL_PREFER_MINM_OVER_MAXP or RADEON_PLL_USE_FRAC_FB_DIV pll flags in
> atombios_adjust_pll().

I'll have a look.

> What link speed and number of lanes are being used for that mode?  Does the
> monitor support downspread?

Easy there :), this whole area is very new to me. "Last week" I figured out
some things about connector probing, anything on top of that still needs to be
learned.

> Does the proprietary driver work ok with that monitor?

I can and will try.

> > Is testing with tiling disabled relevant given the problem happens also without
> > X running?
> 
> That should be equivalent.

Not sure I understand what do you mean by this?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

--- Comment #5 from Alex Deucher <agd5f@yahoo.com> 2012-04-16 09:10:51 PDT ---
(In reply to comment #4)
> 
> > > Is testing with tiling disabled relevant given the problem happens also without
> > > X running?
> > 
> > That should be equivalent.
> 
> Not sure I understand what do you mean by this?

fbdev is linear so that should be equivalent to running X with tiling disabled;
so need to test with tiling disabled.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #6 from Alex Deucher <agd5f@yahoo.com> 2012-04-16 09:11:15 PDT ---
(In reply to comment #5)

> fbdev is linear so that should be equivalent to running X with tiling disabled;
> so need to test with tiling disabled.

so NO need to test with tiling disabled.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #7 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-17 03:20:39 PDT ---
(In reply to comment #3)
> Does the proprietary driver work ok with that monitor?

It doesn't. In fact it is even worse than the open source driver which works OK
in 1920x1200, while fglrx has the same symptoms there (and at any higher
resolution) as open source at 2560x1440.

Where does this finding leads us? According to the specifications
(http://www.amd.com/us/products/notebook/graphics/amd-radeon-6000m/amd-radeon-6300m/pages/amd-radeon-6300m.aspx#2)
this resolution over DP should work. Is it possible for the motherboard vendor
to mess things up in some way?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #8 from Alex Deucher <agd5f@yahoo.com> 2012-04-17 06:18:13 PDT ---
(In reply to comment #7)
> Where does this finding leads us? According to the specifications
> (http://www.amd.com/us/products/notebook/graphics/amd-radeon-6000m/amd-radeon-6300m/pages/amd-radeon-6300m.aspx#2)
> this resolution over DP should work. Is it possible for the motherboard vendor
> to mess things up in some way?

That's the max theoretical mode supported by the chip.  Whether or not you can
drive a monitor that big probably depends on the type and speed of dram in your
system since the GPU (display controllers, 3D engine, etc.) and the CPU have to
share dram bandwidth.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #9 from Roland Scheidegger <sroland@vmware.com> 2012-04-18 14:21:14 PDT ---
(In reply to comment #8)
> That's the max theoretical mode supported by the chip.  Whether or not you can
> drive a monitor that big probably depends on the type and speed of dram in your
> system since the GPU (display controllers, 3D engine, etc.) and the CPU have to
> share dram bandwidth.

I never really understood this problem, not since the days of sdr. Single
channel ddr3-1066 provides roughly 8 times the raw bandwidth of what a
2560x1440 resolution (at 32bpp, 60hz) needs so that should be plenty to serve
other MC clients as well (with lesser priority). So what's the problem there,
too small buffer size for scanout?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #10 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-20 03:43:13 PDT ---
Does the driver know it's memory bandwidth so it could remove modes it cannot
drive from the list?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #11 from Alex Deucher <agd5f@yahoo.com> 2012-04-20 08:19:54 PDT ---
(In reply to comment #9)
> 
> I never really understood this problem, not since the days of sdr. Single
> channel ddr3-1066 provides roughly 8 times the raw bandwidth of what a
> 2560x1440 resolution (at 32bpp, 60hz) needs so that should be plenty to serve
> other MC clients as well (with lesser priority). So what's the problem there,
> too small buffer size for scanout?

I'm just speculating.  I suspect it's more of a latency/timing thing than
bandwidth.  If the request is not there when the LB needs it, it'll run dry.

(In reply to comment #10)
> Does the driver know it's memory bandwidth so it could remove modes it cannot
> drive from the list?

It could and does in some cases and there's even code to check it in the
watermark setup although it probably needs a bit of tweaking for APUs. 
Unfortunately the way the drm is structured makes it hard to do a good job
since modesetting is per crtc so you only get a partial picture.  I'll talk to
the display team and see what they have to say.

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #12 from Alex Deucher <agd5f@yahoo.com> 2012-04-20 12:01:54 PDT ---
Can you attach the xorg log and dmesg output with the DP monitor attached? 
What's the modeline for the 2560x1440 mode?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #13 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-23 00:49:03 PDT ---
Created attachment 60472
  --> https://bugs.freedesktop.org/attachment.cgi?id=60472
Xorg log running 2560x1440

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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--- Comment #14 from Tvrtko Ursulin <tvrtko.ursulin@onelan.co.uk> 2012-04-23 00:52:30 PDT ---
Created attachment 60473
  --> https://bugs.freedesktop.org/attachment.cgi?id=60473
DRM related kernel messages

Is this what you had in mind or would you like something more?

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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Alex Deucher <agd5f@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #60472|text/x-log                  |text/plain
          mime type|                            |
  Attachment #60472|0                           |1
           is patch|                            |

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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Alex Deucher <agd5f@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
  Attachment #60473|text/x-log                  |text/plain
          mime type|                            |
  Attachment #60473|0                           |1
           is patch|                            |

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[Bug 48772] Signal unstable over Display Port on 2560x1440 monitor

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https://bugs.freedesktop.org/show_bug.cgi?id=48772

--- Comment #15 from Andy Pillip <andy@madspunky.net> ---
I do have the same issue on Gnome 3, Wayland, F22 with an Intel Graphics Chip.

On 3840 I see the flashes quite often, and the screen sometimes turns off
completely.

On 2560 it's less flashes, and on 1920 they are gone completely.

I tried different DP connections, because I thought it might be the docking
station that has not enough bandwidth, but also the internal miniDP had that
issue.

I cannot provide a Xorg log, since I'm using Wayland.

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--- Comment #16 from Grigori Goronzy <greg@chown.ath.cx> ---
Note that this could also be a cable issue. Bad quality DP cables are prone to
cause various display issues. I once had a bad cable that even had trouble
driving standard 1080p without dropouts. So maybe just try another cable.

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--- Comment #17 from Andy Pillip <andy@madspunky.net> ---
This is not a cable issue.

I just figured out that for me the issue only occurs on a dual screen setup.

Now I'm running the 3840 resolution on my external screen while switching off
the internal one – without any issues.

Tvrtko, do you have a dual or single setup?

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Martin Peres <martin.peres@free.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |MOVED

--- Comment #18 from Martin Peres <martin.peres@free.fr> ---
-- GitLab Migration Automatic Message --

This bug has been migrated to freedesktop.org's GitLab instance and has been
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You can subscribe and participate further through the new bug through this link
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