[Bug 81476] three monitors on two radeon cards works with some layouts not others

[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

Alex Deucher <agd5f@yahoo.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|xorg-driver-ati@lists.x.org |dri-devel@lists.freedesktop
                   |                            |.org
         QA Contact|xorg-team@lists.x.org       |
            Product|xorg                        |DRI
            Version|7.7 (2011)                  |unspecified
          Component|Driver/Radeon               |DRM/Radeon

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #12 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #11)
> Does this kernel patch help?

I haven't built a kernel from source in years.
Let's see if I still remember how to do this.

I've fetched the Ubuntu kernel source.
Found /usr/src/linux-lts-trusty-3.13.0/drivers/gpu/drm/radeon/radeon_display.c
I've made the edit. (Was line 1422 in my file, not 1547 as in yours.)
Now "make oldconfig" and "make all" and wait...

I'll let you know.
Thanks for the quick action on this.
I see you're the co-author on this file; nice to meet you!

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #13 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #11)
> Does this kernel patch help?

Not with my problem.

1. It doesn't fix the bug and make my desktop work across three monitors.
2. It doesn't prevent all the configurations that can trigger the bug.
3. It does prevent some valid configurations that used to work before.

With your patch, xrandr shows the new smaller screen maximum:

    Screen 0: minimum 320 x 200, current 4096 x 1200, maximum 4096 x 4096
    DVI-0 connected 1600x1200+0+0 
    DVI-1 connected 1600x1200+1600+0 
    DVI-1-2 connected 1600x1200+2496+0 
    DVI-1-3 disconnected

The +2432 offset still works fine across three monitors, as it did before:

    xrandr --output DVI-1-2 --pos 2432x0 --auto

Offsets from +2433 to +2496 are still allowed and still trigger the bug and
cause video crap on the first two monitors, just as they did before.

Offsets above +2496 are now prohibited due to the new smaller screen maximum,
even though I know they would work if I rotated or inverted the first two
monitors.

Your patch doesn't fix the bug.  It does prevent me from using the actual
available screen resolution, should I want to invert or rotate the first two
monitors.  Functionality is lost.

I gather you don't know how to fix the bug, so you're instead trying to limit
the inputs so as not to not let people trigger it?

You said "Rotation uses an additional buffer for each display".  I guess I'll
have to go through the code and find out how to make the non-inverted outputs
use the same type of buffering as the inverted outputs for widths above 4064. 
That should work.

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #14 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #13)
> I guess I'll have to go through the code and find out how to make the
> non-inverted outputs use the same type of buffering as the inverted
> outputs for widths above 4064.

This looks like too much work; I'm not a graphics card programmer.  It would be
faster for me to give away these two old FireMV cards and buy a single modern
card that Linux X11 supports with three 1600x1200 DVI monitors and full 3D (no
Xinerama).  Alex - does AMD have anything like this?

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #15 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #14)
> a single modern card that Linux X11 supports with three 1600x1200 DVI
> monitors and full 3D (no Xinerama).

Phoronix suggests that the open source drivers work well on Radeon HD 6000
cards: http://www.phoronix.com/vr.php?view=20509

"If you find a good deal on a Radeon HD 6000 series GPU (outside of the HD 6900
series), that's where open-source fans will best likely be served".

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #16 from Alex Deucher <agd5f@yahoo.com> ---
(In reply to comment #14)
> 
> This looks like too much work; I'm not a graphics card programmer.  It would
> be faster for me to give away these two old FireMV cards and buy a single
> modern card that Linux X11 supports with three 1600x1200 DVI monitors and
> full 3D (no Xinerama).  Alex - does AMD have anything like this?

All evergreen (hd 5000 series) and newer dGPUs can support up to 6 monitors
depending on the board.

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #17 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #16)
> All evergreen (hd 5000 series) and newer dGPUs can support up to 6
> monitors depending on the board.

Phoronix suggests they don't all work well with open source drivers, those that
do work often don't do well multi-monitor, and most don't do triple DVI output
unless one buys one or more active adapters.

I don't want to pick a card that becomes obsolete and where the driver writers
have moved on and aren't interested in fixing the old bugs (e.g. the above bug
in the radeon driver).

Are the open source drivers for the evergreen cards (and newer) under active
development?

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #18 from Alex Deucher <agd5f@yahoo.com> ---
(In reply to comment #17)
> 
> Phoronix suggests they don't all work well with open source drivers, those
> that do work often don't do well multi-monitor, and most don't do triple DVI
> output unless one buys one or more active adapters.

Displays should generally work fine.  Note that Evergreen, NI, and SI parts
only have two non-DP PLLs so they are limited to two independent non-DP clocks.
 So what this means is that you can only use two non-DP monitors with
independent timings.  If you want to use more than two non-DP monitors, you
have to use the exact same pixel clocks on several of the monitors so you don't
use more then two different clocks.  E.g., if all three of your monitors are
identical use the same modeline and pixel clock, you'd only need one PLL so you
should be fine.

> 
> I don't want to pick a card that becomes obsolete and where the driver
> writers have moved on and aren't interested in fixing the old bugs (e.g. the
> above bug in the radeon driver).

TBH, I think it's a hw limitation on r5xx hardware that's not properly handled.
 Unfortunately, X didn't support multi-card xrandr support when r5xx was still
actively being developed.  At that time, the only way to support multi-card
multi-head was zaphod mode which uses separate buffers for each display so you
never hit the hw limits.

> 
> Are the open source drivers for the evergreen cards (and newer) under active
> development?

Yes.

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #19 from Ian! D. Allen <idallen@idallen.ca> ---
(In reply to comment #18)
> if all three of your monitors are identical use the same modeline and
> pixel clock, you'd only need one PLL so you should be fine.

Yes: Three identical 1600x1200.  I just have to find an available card that can
handle three DVI connectors, ideally without having to buy an active adapter. 
(Sapphire makes a "Flex" card that claims to do this; my initial attempts to
find one to buy have turned up nothing useful.)

> TBH, I think it's a hw limitation on r5xx hardware that's not properly handled.

I'd believe it as a hardware limitation if inverting the first two monitors
didn't fix it.  If I were willing to physically turn my first two monitors
upside-down, it would work fine with the given hardware.  The hardware can
display across my three monitors at 4800x1200 as long as two of the screens are
inverted.  We just need to make the software put those screens into the
hardware the other way up!

Thanks for your comments.

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #20 from Alex Deucher <agd5f@yahoo.com> ---
(In reply to comment #19)
> 
> I'd believe it as a hardware limitation if inverting the first two monitors
> didn't fix it.  If I were willing to physically turn my first two monitors
> upside-down, it would work fine with the given hardware.  The hardware can
> display across my three monitors at 4800x1200 as long as two of the screens
> are inverted.  We just need to make the software put those screens into the
> hardware the other way up!

As I said before, it only works with rotation because it's scanning out of
different buffers when rotation is enabled.  When you enable rotation a shadow
buffer is created which is a rotated duplicate of the sub-region of the entire
desktop.  So for the rotated case, the display hw is scanning out of a
1600x1200 surface rather than the full 4800x1200 surface.  If you wanted to you
could do something similar for the non-rotated case in the xserver, but that
would incur an extra copy for every update of the desktop in the non-rotated
case.

If you want to test further, try and disable acceleration (Option "NoAccel"
"true" in the device section of your xorg.conf) or use the modesetting driver
(xf86-video-modesetting).  You won't be able to use rotation since that
requires acceleration do to the rotated blit, but that will take all
non-display hw factors (3D, etc.) out of the equation.

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[Bug 81476] three monitors on two radeon cards works with some layouts not others

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https://bugs.freedesktop.org/show_bug.cgi?id=81476

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

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

--- Comment #21 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
to our GitLab instance: https://gitlab.freedesktop.org/drm/amd/issues/511.

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