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Bug 229652 - can't use 1920x1200 resolution and 24 bit color with XEN kernel
Summary: can't use 1920x1200 resolution and 24 bit color with XEN kernel
Alias: None
Product: Fedora
Classification: Fedora
Component: kernel
Version: 6
Hardware: i386
OS: Linux
Target Milestone: ---
Assignee: Adam Jackson
QA Contact: Brian Brock
Depends On:
TreeView+ depends on / blocked
Reported: 2007-02-22 14:58 UTC by David Juran
Modified: 2007-11-30 22:11 UTC (History)
4 users (show)

Fixed In Version: xorg-x11-drv-i810-2.0.0-4.fc7
Doc Type: Bug Fix
Doc Text:
Clone Of:
Last Closed: 2007-07-03 16:04:30 UTC

Attachments (Terms of Use)
Xorg.log (deleted)
2007-02-22 15:00 UTC, David Juran
no flags Details
X log from vanilla kernel for comparison (deleted)
2007-02-27 15:55 UTC, David Juran
no flags Details

Description David Juran 2007-02-22 14:58:51 UTC
From Bugzilla Helper:
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20070209 Fedora/ Firefox/ pango-text

Description of problem:
I have a Intel 945GM graphics adaptor in my Dell D820 laptop and a screen capable of 1920x1200. I use the i810 driver (when trying the "intel" one I only get a black screen) and use the 915resolution utility to patch mode 5c to 1920x1200. And everything works fine _until_ I boot the Xen kernel (2.6.19-1.2911.fc6xen). With the XEN kernel I only get the 1600x1200 resolution.... Does anyone have any clues? Attached is the Xorg.log.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. boot XEN kernel

Actual Results:

Expected Results:

Additional info:

Comment 1 David Juran 2007-02-22 15:00:02 UTC
Created attachment 148570 [details]

Comment 2 David Juran 2007-02-27 10:04:30 UTC
In BIOS on my laptop, there is an option to set "LCD panel expansion" to "off".
When set to this, the display will show a small but sharp image centered on the
screen when driven with a low resolution. I've noticed that when running the Xen
kernel, if I switch back to a VT _after_ X has started the image of the VT is
then stretched to cover the entire screen giving a blurry image. Not a major
problem per se, but maybe a hint of what's wrong...

Comment 3 David Juran 2007-02-27 15:55:25 UTC
Created attachment 148868 [details]
X log from vanilla kernel for comparison

Comment 4 David Juran 2007-02-27 16:49:03 UTC
Discussing this with the X-people we (surprisingly) came to the conclusion this
probably a (XEN) kernel problem.... So to re-iterate the issue. If I boot my
Latitude D820 laptop with the vanilla  2.6.19-1.2911.fc6 kernel everything works
fine but if I boot it with the XEN kernel I need to step down to 16 bit colour
in order to get the full 1920x1200 resolution. I use the i810 driver and the
"915resolution" utility to re-map one of the graphics modes to 1920x1200.
I'm attaching the output of dmesg in case it could contain any leads... 

Comment 5 Martin von Weissenberg 2007-03-12 16:20:41 UTC
I have found this same bug, independent of David, and can also reproduce it.

The relevant packages are:



Comment 6 Adam Jackson 2007-03-12 21:08:11 UTC
Just to make the point a bit clearer:

X should not be able to tell the difference between a normal kernel and a
Xen-enabled dom0 Linux kernel; X is a userspace process, and therefore all the
Xen magic _should_ be hidden.  Therefore any visible difference in X's behaviour
between normal and dom0 kernels is highly likely to be a bug in Xen.

For this particular bug, 915resolution maps part of the video BIOS and scribbles
in new timings; later, X comes along and asks the video BIOS to set that mode. 
That the new timings don't make it to X, indicates that Xen's mmap code is
busted for this case.

Comment 7 Martin von Weissenberg 2007-03-13 08:53:17 UTC
I'm not sure about the mmap interpretation. The 1920x1200x16 resolution wouldn't
be available unless 915resolution did something.

Without 915resolution the screen resolution is limited to 1600x1200 for all
color depths. Using 915resolution I get 1920x1200 at all color depths. Booting
the Xen kernel and using 915resolution, I get 1600x1200 at 24 bit, but lowering
the depth to 16 bits gives 1920x1200.

Comment 8 Stephen Tweedie 2007-03-13 15:45:33 UTC
Right; it looks more like the different memory layout under Xen is confusing
something into thinking that there's less framebuffer memory available.  That's
the only reason I can think of why 1920x1200x24 wouldn't be available if it's
available at ...x16 (the video timings are the same for both).

Checks... and indeed, the Xorg.log shows

(II) I810(0): Modeline "1920x1200"  161.84  1920 2020 2052 2184  1200 1202 1208
1235 -hsync -vsync
(--) I810(0): A non-CRT device is attached to pipe B.
	No refresh rate overrides will be attempted.
(--) I810(0): Maximum space available for video modes: 7872 kByte

so it IS detecting 1920x1200, but is only offering 7.8MB for video memory; the
non-Xen case shows 

(--) I810(0): Maximum space available for video modes: 12288 kByte

for the memory detection.

To proceed, we'd need to know how X determines the maximum available memory in
this case.  Once we've got that, we can certainly look into why it's different
under Xen.

Comment 9 Adam Jackson 2007-03-14 22:02:54 UTC
The i810 driver queries memory size from VBE.  If it's too small, it makes
another VBE call to allocate more, and then reinits VBE.  Apparently under Xen
this change isn't taking effect.

This could be due to using the x86 emulator instead of vm86 when in Xen, but we
had to do that at one point because Xen's vm86 support was so deeply broken.  It
would be interesting to know if the same failure shows under non-xen kernel when
using the x86 emulator.  You'd do this by adding the line

Option "Int10Backend" "x86emu"

to the ServerLayout section in xorg.conf.

Comment 10 Martin von Weissenberg 2007-03-15 08:02:47 UTC
Adding the x86emu line to xorg.conf results again in 1600x1200. This is with
915resolution and without Xen.

(II) I810(0): Printing DDC gathered Modelines:
(II) I810(0): Modeline "1920x1200"  161.84  1920 2020 2052 2184  1200 1202 1208 
1235 -hsync -vsync
(--) I810(0): A non-CRT device is attached to pipe B.
        No refresh rate overrides will be attempted.
(--) I810(0): Maximum space available for video modes: 7872 kByte

Comment 11 David Juran 2007-07-03 16:04:30 UTC
In Fedora 7, with kernel-xen-2.6.20-2925.11.fc7, and the intel (not i810 driver)
from xorg-x11-drv-i810-2.0.0-4.fc7 everything works fine so I'm closing this bug(-:

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