Difference in dot clock between xserver 1.5.2 and 1.9.4 - intel driver

Difference in dot clock between xserver 1.5.2 and 1.9.4 - intel driver

[SD]

Dear All

I have ONE laptop with ONE hdd and 2 OS - opensuse and fedora on it.
When I boot opensuse LCD picture is perfect but is not on fedora.
My video is i915GM.
I would like to show one difference in xorg log:

X.Org X Server 1.5.2
Release Date: 10 October 2008
X Protocol Version 11, Revision 0
Build Operating System: openSUSE SUSE LINUX
Current Operating System: Linux linux-xmc2 2.6.27.45-0.1-pae #1 SMP 2010-02-22 16:49:47 +0100 i686
...
(II) intel(0): using SSC reference clock of 96 MHz
************************************************************

X.Org X Server 1.9.4
Release Date: 2011-02-04
[    22.536] X Protocol Version 11, Revision 0
[    22.536] Build Operating System: x86-06 2.6.32-71.14.1.el6.x86_64 
[    22.536] Current Operating System: Linux f14.fedora14 2.6.35.11-83.fc14.i686.PAE #1 SMP Mon Feb 7 06:57:55 UTC 2011 i686
...
[   135.556] (II) intel(0): Supported detailed timing:
[   135.556] (II) intel(0): clock: 65.0 MHz   Image Size:  304 x 228 mm

**************************************************************


On OpenSuse, where I can use clock is 96 MHZ, on Fedora it is 65 MHz.
Why?

And in MHz can be only dot clock, but if I use 1024x768x60Hz = ~ 47.2 MHz and we need to multiply on 3 (subpixels), it will be ~140 MHz
I know that 96 in xserver 1.5.2 is not 140 but it is much closer to it, then 65.

Why in xserver 1.5.2 intel driver shows 96 MHz but in 1.9.4 it does only 65 MHz. And can it be the reason why my LCD shows picture like it use less then 50Hz vsync.

Thank you.

Re: Difference in dot clock between xserver 1.5.2 and 1.9.4 - intel driver

[Keith Packard]

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On Mon, 28 Feb 2011 03:54:24 -0800 (PST), SD <sd.domrep@yahoo.com> wrote:

> (II) intel(0): using SSC reference clock of 96 MHz

That's the spread-spectrum clock reference value; it forms the basis
From which the actual dot clock is computed using a PLL. It is *not* the
actual dot clock.


> [   135.556] (II) intel(0): clock: 65.0 MHz   Image Size:  304 x 228
> mm

And there's the actual dot clock.

> And in MHz can be only dot clock, but if I use 1024x768x60Hz = ~ 47.2 MHz and we need to multiply on 3 (subpixels), it will be ~140 MHz
> I know that 96 in xserver 1.5.2 is not 140 but it is much closer to
> it, then 65.

You don't multiply by three; each channel has it's own wire in
LVDS. But, you have to add space for the retrace intervals. The standard
VESA mode for 1024x768x60 uses a 65MHz dot clock.

> Why in xserver 1.5.2 intel driver shows 96 MHz but in 1.9.4 it does
> only 65 MHz. And can it be the reason why my LCD shows picture like it
> use less then 50Hz vsync.

I'll bet both are using the same timings, but you can check for yourself
with the 'xrandr' utility:

$ xrandr --verbose
...
  1440x900 (0x45)   74.1MHz -HSync -VSync *current +preferred
        h: width  1440 start 1464 end 1480 total 1600 skew    0 clock   46.3KHz
        v: height  900 start  903 end  909 total  926           clock   50.0Hz
...

The mode marked '*current' is what the system is currently using.

You can help figure out what the problem is by running the
'intel_reg_dumper' utility on both distributions. That's available from:

git://anongit.freedesktop.org/git/xorg/app/intel-gpu-tools

Doing a 'diff' on the output of this under the two operating systems
will show every change in programming for your machine.

-- 
keith.packard@intel.com

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