Bug 433123 - dpi is incorrect for physical size
dpi is incorrect for physical size
Product: Fedora
Classification: Fedora
Component: xorg-x11-drv-ati (Show other bugs)
i386 Linux
low Severity low
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Assigned To: Dave Airlie
Fedora Extras Quality Assurance
Depends On:
  Show dependency treegraph
Reported: 2008-02-16 11:09 EST by darrell pfeifer
Modified: 2009-10-22 08:44 EDT (History)
5 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2009-02-07 11:35:30 EST
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Verified Versions:
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

Attachments (Terms of Use)
Xorg.0.log (34.84 KB, text/plain)
2008-02-16 12:55 EST, darrell pfeifer
no flags Details
xorg.conf (1.13 KB, text/plain)
2008-02-18 10:09 EST, darrell pfeifer
no flags Details

  None (edit)
Description darrell pfeifer 2008-02-16 11:09:47 EST
Description of problem:

The radeon driver reports an incorrect DPI. This causes huge firefox/minefield
to produce really huge icons and screen images.

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


How reproducible:

Steps to Reproduce:
Actual results:

xrdb -query | grep dpi
Xft.dpi:	120


screen #0:
  dimensions:    1920x1200 pixels (300x230 millimeters)
  resolution:    163x133 dots per inch

Expected results:

Physical size of the screen is 14.5 inches (368 mm) by 9 inches, so dpi should
be 133/134 in both dimensions.

Additional info:

01:00.0 VGA compatible controller: ATI Technologies Inc M22 [Mobility Radeon X300]
Comment 1 Felix Miata 2008-02-16 11:57:18 EST
Upstream Gecko issues: https://bugzilla.mozilla.org/show_bug.cgi?id=378927

Mailing list thread:

What reporter is describing is 17" WUXGA display, about the highest available
DPI in currently marketed mainstream hardware.
Comment 2 darrell pfeifer 2008-02-16 12:55:41 EST
Created attachment 295078 [details]
Comment 3 Felix Miata 2008-02-16 13:21:24 EST
Somebody please change attachment to a valid type. It won't let me do it.
Comment 4 Andrew Farris 2008-02-17 01:50:33 EST
Hmm, I'm seeing something similar with vmware driver and I have a much lower resolution display 

I noticed that the system->preferences->appearance dialog now includes a dpi selector which 
changes the xft.dpi setting dynamically.  My display was showing what I thought was 'normal' dpi until I 
opened the appearance tool today and then suddenly my fonts all got much bigger (it had chosen to 
change to 140dpi).  This was for the entire gnome interface, not just firefox, just so we are clear.  I have 
previously set the firefox dpi to be 120 manually in about:config because of the issues with it detecting 

My screen should be 113x112 dpi by its dimensions... and xdpyinfo is reporting 153x128 dpi because 
the dimensions are wrong; it reports 212x159mm (8.34"x6.26") while my screen size is really 
11.25"x7.1".  This is a black 13" macbook.  The xorg log shows selecting 96x96 dpi but it is starting in 
a different resolution, which changes when I login (set to 1280x800 for this user).

So, it looks like either the vmware driver has a bug as well, or something is effecting both these drivers 
(and only recently).  That new dialog option to set the dpi is recent if I'm not mistaken.
Comment 5 Matěj Cepl 2008-02-17 12:45:44 EST
I am not sure whether component is right, but passing to developers.
Comment 6 Adam Jackson 2008-02-18 09:57:35 EST
Just so we're clear here:  The DPI setting for xft is simply a scale factor.  It
is not inferred from the physical DPI.  It is specified as DPI for historical
reasons only.

I assume this is because the radeon driver is guessing wildly at your display
size (since you don't seem to have an EDID block for your internal panel), and
is doing the guessing wrong.  The physical size it's guessing is 4:3 even though
the display is 16:10.  So this is likely to be a bug in the radeon driver, but
just to be sure, please attach your xorg.conf so we can check if you're
accidentally setting a display size there.
Comment 7 darrell pfeifer 2008-02-18 10:09:10 EST
Created attachment 295172 [details]
Comment 8 Adam Jackson 2008-03-06 15:17:20 EST
Right, definitely a radeon bug then.
Comment 9 Charles R. Anderson 2008-04-07 15:13:13 EDT
I have two Dell 2001FP 21" LCD panels connected to a Radeon X600.  The panels
are each 408x306mm as I measured myself.  Xorg.0.log says:

(II) RADEON(0): EDID vendor "DEL", prod id 40968
(II) RADEON(0): Output DVI-1 connected
(II) RADEON(0): Output DVI-0 connected
(II) RADEON(0): Using exact sizes for initial modes
(II) RADEON(0): Output DVI-1 using initial mode 1600x1200
(II) RADEON(0): Output DVI-0 using initial mode 1600x1200
after xf86InitialConfiguration
(**) RADEON(0): Display dimensions: (410, 310) mm
(**) RADEON(0): DPI set to (198, 131)

xrandr says:

DVI-0 connected 1600x1200+0+0 (normal left inverted right x axis y axis) 367mm x

and the same for DVI-1.

Comment 10 Charles R. Anderson 2008-04-08 22:07:04 EDT
Everytime I log in, I have to "xrandr -dpi 100" and then restart Firefox to get
it to a normal size.
Comment 11 Andrew Farris 2008-04-08 22:30:09 EDT
@Charles, not a fix, but you could add this to .bashrc to ease the pain:
if [ $DISPLAY ]; then xrandr --dpi 100; fi
Comment 12 Bug Zapper 2008-05-14 01:14:01 EDT
Changing version to '9' as part of upcoming Fedora 9 GA.
More information and reason for this action is here:
Comment 13 François Cami 2009-02-07 10:43:35 EST
I can't reproduce on Fedora 10.
Darrell, could you confirm that this is fixed on current, fully patched F10 ?
If you have trouble booting, please use  nomodeset   in the kernel command line.
Thanks in advance.
Comment 14 darrell pfeifer 2009-02-07 11:35:30 EST
This is fixed in F10.

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