Comment 1 for bug 1568104

I got this comment from Steven Chamberlain (Debian GNU/kFreeBSD developer):

On Sun, Apr 17, 2016 at 02:57:07PM +0100, Steven Chamberlain wrote:
> Hi!
>
> (I'm not registered on Launchpad, so mailing you directly...)
>
> In reply to
> https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/1568104
>
> it seems to be a problem with xserver-xorg-video-qxl, not the Xorg
> server itself.
>
> Firstly:
>
> | [ 144.925] (II) [KMS] drm report modesetting isn't supported.
>
> may be expected, if the FreeBSD kernel does not have a KMS driver for
> QXL. The detection happens in
> http://sources.debian.net/src/libdrm/2.4.58-2/xf86drmMode.c/?hl=724#L776
> which mainly looks at a sysctl hw.dri.*.modesetting to ask the kernel of
> KMS is enabled or not. (Maybe the original reporter could share his
> output of `sysctl hw.dri` to confirm this).
>
> Without that, it falls back to some other mode of operation. It seems
> to attempt some kind of direct memory-mapped I/O, and maybe that code is
> unsuitable for kFreeBSD:
>
> | [ 145.095] (EE) Backtrace:
> | [ 145.096] (EE) 0: /usr/bin/X (xorg_backtrace+0x4e) [0x58cc8e]
> | [ 145.096] (EE) 1: /usr/bin/X (0x400000+0x191009) [0x591009]
> | [ 145.096] (EE) 2: ?? [0x7ffffffff043]
> | [ 145.096] (EE) 3: /usr/lib/x86_64-kfreebsd-gnu/libpciaccess.so.0
> | (pci_io_write8+0x3) [0x80104e203]
> | [ 145.096] (EE) 4: /usr/lib/xorg/modules/drivers/qxl_drv.so
> | (0x8055a5000+0xb530) [0x8055b0530]
> | [ 145.096] (EE) 5: /usr/lib/xorg/modules/drivers/qxl_drv.so
> | (0x8055a5000+0x7811) [0x8055ac811]
>
> (Installing package xserver-xorg-video-qxl-dbg might give a more
> detailed backtrace).
>
> However, if kFreeBSD doesn't support KMS with QXL, maybe it has no
> advantage over plain VESA mode? I would consider disabling/uninstalling
> the QXL driver, if it can't be easily fixed for kFreeBSD. Then Xorg
> would fall back to VESA mode and not crash.
>
> Regards,
> --
> Steven Chamberlain
> <email address hidden>