mtx + Matrox P650 + XF86VidModeSetGammaRamp() problems ?

Alex Deucher alexdeucher at
Wed Apr 4 20:50:42 PDT 2007

On 4/4/07, Graeme Gill <graeme2 at> wrote:
> I have a couple of reports from people with Matrox P650 cards
> that even though these cards are advertised as having dual
> VideoLuts (one for each output), that there is no effect
> on the output (DVI in particular) in setting the Luts
> using XF86VidModeSetGammaRamp(). There is some disappointment,
> since this was why this particular card was purchased, to allow
> proper screen calibration.

Most recent hardware had independent LUTs for each crtc.

> Can anyone shed any light on this, or point to an appropriate
> place to get some answers ? (I don't actually have one
> of these cards or I'd look into it more myself).

I'm guessing their driver either ignores the request or doesn't
implement the functionality in some cases.  Unfortunately since the
driver is closed source about all you can do is complain to matrox.
If the user is using some mergedfb type multi-head functionality,
XF86VidModeSetGammaRamp() will propably only update one or both sets
of LUTs as it has no concept of multiple crtcs or LUTs.  This will be
the case with most drivers until they get proper randr 1.2 support.
Xinerama screen based multi-head may work as there are actually
multiple underlying screens.  It all depends on the driver though.


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