Configuring xrandr: too small screen size?

[Alex Deucher]

On Sun, May 23, 2010 at 11:56 AM, Dotan Cohen <dotancohen at gmail.com> wrote:
> I have a Dell Inspiron 6400 / 1505E with 1680x1050 built-in LVDS and
> external VGA connected to a 1680x1050 LCD monitor. The machine has an
> ATI MobileRadeon x1400 graphics card, radeon driver. I can get the
> external monitor to mirror the regular display, but I cannot put them
> side-by-side with xrandr.
>
> ✈dcl:~$ xrandr --output LVDS1 --auto --preferred --output VGA1 --auto
> --left-of LVDS1
> ✈dcl:~$ xrandr --fb 3360x1050
> xrandr: screen cannot be larger than 1680x1680 (desired size 3360x1050)
> ✈dcl:~$ xrandr --fb 1680x2100
> xrandr: screen cannot be larger than 1680x1680 (desired size 1680x2100)
>
> The first command has absolutely no effect, that is why I try the
> other two. Any ideas what to try next? Thanks!
>

The ums (userspace modesetting) radeon driver cannot resize the front
buffer after X has started.  You need to either pre-allocate a larger
front buffer using a Virtual directive in your xorg.conf, or enable
kms (kernel modesetting).  The kms-enabled radeon driver supports
buffer resizing.

Alex

> --
> Dotan Cohen
>
> http://gibberish.co.il
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