Nouveau - Jan 2009 - [Bug 19854] New: xscreensaver fails to run (regression)

http://bugs.freedesktop.org/show_bug.cgi?id=19854

           Summary: xscreensaver fails to run (regression)
           Product: xorg
           Version: 7.4
          Platform: Other
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/nouveau
        AssignedTo: nouveau at lists.freedesktop.org
        ReportedBy: jsagarribay at gmail.com
         QAContact: xorg-team at lists.x.org


xscreensaver spits the following error:

##############################################################################

xscreensaver: 11:01:03: X Error!  PLEASE REPORT THIS BUG.

##############################################################################

X Error of failed request:  174
  Major opcode of failed request:  152 (RANDR)
  Minor opcode of failed request:  20 ()
  Serial number of failed request:  76
  Current serial number in output stream:  76

After bisecting the driver, it turns out this is the first bad commit:

commit 599d258948be0505f02947251ad6877e7168d9a8
Author: Stuart Bennett <sb476 at cam.ac.uk>
Date:   Mon Aug 25 01:47:45 2008 +0100

    randr12: multiple encoders per connector (DVI-I)

This is with a Geforce Go 7300


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--- Comment #1 from Stuart Bennett <sb476 at cam.ac.uk>  2009-02-01
19:35:49 PST ---
This looks like http://bugs.gentoo.org/249680 , where xscreensaver does the
wrong thing on outputs without a crtc.  Try the patch to xscreensaver in that
bug and if it fixes it, take it up with the xscreensaver maintainer.


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Jaime Velasco Juan <jsagarribay at gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|xscreensaver fails to run   |XrandR reports no CRTCs for
                   |(regression)                |VGA-0 output until the first
                   |                            |time a display is plugged




--- Comment #2 from Jaime Velasco Juan <jsagarribay at gmail.com> 
2009-02-06 04:36:55 PST ---
Yep, the bug seems the same (I haven't had the time to compile xscreensaver
yet), however I think that nouveau may be at fault here:

1) X starts whith only LVDS connected
2) XrandR reports no CRTCs for VGA-0 output. I'd expect it to report CRTCs 0
and 1, as both of them can drive the output when it is connected (and this is
what it did before, IIRC)
3) xscreensaver fails.

If at this point one runs xrandr --addmode VGA-0 640x480, the server crashes
with
Backtrace:
0: /usr/bin/X(xorg_backtrace+0x26) [0x4ebd56]
1: /usr/bin/X(xf86SigHandler+0x39) [0x47f949]
2: /lib/libc.so.6 [0x7f637896ef80]
3: /usr/lib/xorg/modules/drivers//nouveau_drv.so [0x7f63773c2fe6]
4: /usr/bin/X [0x4adfbb]
5: /usr/bin/X(RROutputAddUserMode+0xa4) [0x525d64]
6: /usr/bin/X(Dispatch+0x364) [0x44c2d4]
7: /usr/bin/X(main+0x45d) [0x432bcd]
8: /lib/libc.so.6(__libc_start_main+0xe6) [0x7f637895b1a6]
9: /usr/bin/X(FontFileCompleteXLFD+0x269) [0x431fa9]

Fatal server error:
Caught signal 11.  Server aborting

inside nv_output_mode_valid (I think nv_encoder is NULL at this point).

When a display is connected to VGA-0, xrandr reports CRTCs: 0 1 for VGA-0, and
everything works as it should (xscreensaver included). If the display is
disconnected, everything keeps working (and xrandr --addmode no longer crashes
the server), the CRTCs: 0 1 line remains in the VGA-0 output of xrandr.

So, I don't know for sure if it is wrong to report no CRTCs for a
disconnected
output, but the fact that the reported CRTCs change after an external display
is plugged and unplugged again, and the related crash of the Xserver seems to
imply that there is a bug with this. I've changed the description
accordingly.


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--- Comment #3 from Stuart Bennett <sb476 at cam.ac.uk>  2009-02-07
09:01:52 PST ---
(In reply to comment #2)
> Yep, the bug seems the same (I haven't had the time to compile
xscreensaver
> yet), however I think that nouveau may be at fault here:
> 
> 1) X starts whith only LVDS connected
> 2) XrandR reports no CRTCs for VGA-0 output. I'd expect it to report
CRTCs 0
> and 1, as both of them can drive the output when it is connected (and this
is
> what it did before, IIRC)
> 3) xscreensaver fails.
> 
> If at this point one runs xrandr --addmode VGA-0 640x480, the server
crashes
> with
...
> inside nv_output_mode_valid (I think nv_encoder is NULL at this point).
> 
> When a display is connected to VGA-0, xrandr reports CRTCs: 0 1 for VGA-0,
and
> everything works as it should (xscreensaver included). If the display is
> disconnected, everything keeps working (and xrandr --addmode no longer
crashes
> the server), the CRTCs: 0 1 line remains in the VGA-0 output of xrandr.
> 
> So, I don't know for sure if it is wrong to report no CRTCs for a
disconnected
> output, but the fact that the reported CRTCs change after an external
display
> is plugged and unplugged again, and the related crash of the Xserver seems
to
> imply that there is a bug with this. I've changed the description
accordingly.
Agreed that the crash is a bug, and the <never plugged> vs
<plugged>,<unplugged> inconsistency is an issue.  Can you confirm
the following
patch resolves both these problems?

As for 2) above, while in the VGA-0 case listing CRTCs when disconnected is
possible, it really isn't for DVI-I until a monitor is plugged (as the
available CRTCs vary depending on whether it's an analogue or digital
connection).  I think I'd prefer to retain a consistent approach across all
connector types, and get other things that make bad assumptions get fixed
sooner :-) (is there any real-world case where the usefulness of providing a
crtc list for unused connectors exceeds the problem that it won't work half
the
time (DVI)?)


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--- Comment #4 from Stuart Bennett <sb476 at cam.ac.uk>  2009-02-07
09:03:14 PST ---
Created an attachment (id=22665)
 --> (http://bugs.freedesktop.org/attachment.cgi?id=22665)
Patch against addmode crash, add consistency for outputs unplugged at runtime


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--- Comment #5 from Jaime Velasco Juan <jsagarribay at gmail.com> 
2009-02-10 10:52:58 PST ---
(In reply to comment #3)
Sorry for the delay...
> Agreed that the crash is a bug, and the <never plugged> vs
> <plugged>,<unplugged> inconsistency is an issue.  Can you
confirm the following
> patch resolves both these problems?
> 
It solves the crash, but I can't test with an external display unless I
carry
the laptop to work, which I'd prefer not to do again... maybe there is
someone
else who can reproduce the bug and test the fix?. If not, I'll try to do it
when I can.
> As for 2) above, while in the VGA-0 case listing CRTCs when disconnected is
> possible, it really isn't for DVI-I until a monitor is plugged (as the
> available CRTCs vary depending on whether it's an analogue or digital
> connection).  I think I'd prefer to retain a consistent approach across
all
> connector types, and get other things that make bad assumptions get fixed
> sooner :-) (is there any real-world case where the usefulness of providing
a
> crtc list for unused connectors exceeds the problem that it won't work
half the
> time (DVI)?)
> 
I don't know, the only known problem is with xscreensaver which is arguably
buggy. OTOH if there are cases where a CRTC can't drive some displays, it is
correct to simply return an error at modesetting time, no? (I took a look at
the randr spec, but may be misremembering it). In other words, I'm fine with
whatever you decide to do, I don't know better. :-)


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--- Comment #6 from Stuart Bennett <sb476 at cam.ac.uk>  2009-02-11
10:01:18 PST ---
So, I've pushed the crash fix, but not the state resetting thing.  After
testing it, it seems xrandr gets very upset (even just running xrandr
--verbose) with CRTCs disappearing (although this is probably valid behaviour)
and dies with a fatal error of "cannot find crtc 0x..", so I'll
stick with the
crap lingering CRTC behaviour, rather than break xrandr whenever someone
disconnects an output.

As for bailing out at modeset time, yes, this might be possible, but it relies
on the xserver failing gracefully, and the user app coping with a failure for
which it can determine no good reason, which I think is a higher standard to
expect than getting the application to query what display is connected before
it sets out on its modesetting journey.

Happy for this bug to be resolved as fixed?


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Jaime Velasco Juan <jsagarribay at gmail.com> changed:

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




--- Comment #7 from Jaime Velasco Juan <jsagarribay at gmail.com> 
2009-02-12 09:59:21 PST ---
(In reply to comment #6)
> So, I've pushed the crash fix, but not the state resetting thing. 
After
> testing it, it seems xrandr gets very upset (even just running xrandr
> --verbose) with CRTCs disappearing (although this is probably valid
behaviour)
> and dies with a fatal error of "cannot find crtc 0x..", so
I'll stick with the
> crap lingering CRTC behaviour, rather than break xrandr whenever someone
> disconnects an output.
> 
> As for bailing out at modeset time, yes, this might be possible, but it
relies
> on the xserver failing gracefully, and the user app coping with a failure
for
> which it can determine no good reason, which I think is a higher standard
to
> expect than getting the application to query what display is connected
before
> it sets out on its modesetting journey.
> 
> Happy for this bug to be resolved as fixed?
> 
Yes, thank you. If it turns out this is not really correct it can be reopened
again.


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