Nouveau - Aug 2011 - [Bug 40502] New: Ability to assign arbitrary CRTC to an output is broken

https://bugs.freedesktop.org/show_bug.cgi?id=40502

           Summary: Ability to assign arbitrary CRTC to an output is
                    broken
           Product: xorg
           Version: git
          Platform: x86-64 (AMD64)
        OS/Version: Linux (All)
            Status: NEW
          Severity: minor
          Priority: medium
         Component: Driver/nouveau
        AssignedTo: nouveau at lists.freedesktop.org
        ReportedBy: maximlevitsky at gmail.com
         QAContact: xorg-team at lists.x.org


I am assigning that bug to nouveau DDX, although I really won't be surprised
if
that is xserver or even kernel driver bug.

I have two CRTCs (CRTC0 and CRTC1) (most modern cards have such number)

I would like to assign CRTC1 to laptop screen, so I do this:

xrandr --output LVDS-1 --auto --crtc 1

Screen does blink however doing 'xrandr --verbose' still tells me that
LVDS-1
uses CRTC0.
I can repeat that command again and again.
If I enable kernel modesetting debug, I notice that LVDS-1 is connected once to
CRTC0 and once to CRTC1 (on each invocation of 'xrandr' they change
places),
and it does succedd, leading me to beliving that on kernel level everything is
fine.
However on higher level something is really broken, as xrand insists that
LVDS-1 connected to CRTC0, not to mention that such toggle of CRTCs shouln't
take place as I told explicitly I want to use crtc1.

This is preparation of hunt for bug that causes external connected monitor to
go dark after suspend and resume cycle sometimes, then if I disconnect it, even
nastier problem happends, the notebook screen goes dark as well, a thing that
makes me suspect that one of CRTCs goes tits up.
So I need a ability to control which CRTC is used.


I am using very recent versions (from git actually) of everything related to
GFX stack, although not everything is up to date, like for example xrand
library.

I think I will be able to handle that bug on my own, although if you have seen
anything related, or maybe even fact that this is known, please tell me.

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https://bugs.freedesktop.org/show_bug.cgi?id=40502

--- Comment #1 from maximlevitsky at gmail.com 2011-10-08 02:46:42 PDT ---
So, I understand now what is going on.
Its actually a feature, very unusual and strange one.

When I execute:
'xrandr --output LVDS-1 --auto --crtc 1'

System does switch LVDS to CRTC1, however, xrandr also marks said CRTC as
primary, which brings it to first position of crtc list in
XRRGetScreenResources.
and therefore on next invocation xrandr insists that output is once again
connected to CRTC 0, which is technicaly true, but its different '0'.

Also except reporting actual atom values, there is no way for xrandr to undo
this feature which granted is to support backward compatability with older (and
current?) desktops.

Yet, at least xrandr could sort the crtc list and assuming that atom values for
each crtc don't change (and they seem not) it'll fix this problem.

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https://bugs.freedesktop.org/show_bug.cgi?id=40502

maximlevitsky at gmail.com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|Driver/nouveau              |DDX/xorg
         AssignedTo|nouveau at lists.freedesktop.o |xorg-team at lists.x.org
                   |rg                          |
                 CC|                            |maximlevitsky at gmail.com

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