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Date: Mon, 31 Jul 95 09:36:10 -0400
From: Ted Baker <baker@ada.cs.fsu.edu>
As I said, I can't figure any way to get the Linux SVGA driver to
work with 800 x 600. It reports that it has detected a WD90C24,
but that it does not know how to use that so it is treating it as a
WD90C30. By observation, it is clearly not 100% compatible.
[...]
It seems the clocks are programmable, but the WD90C30 driver seems
to assume they are not. To use the 800x600 resolution I need a
higher dot-clock. Hence, it seems I need to modify the driver.
There is some unusual behavior with the Linux SVGA driver when running
on ThinkPads. First, in order to get an accurate clocks list, you
must connect an external monitor to the 'Pad. I don't know why this
is so, but it has been true for all 'Pads, and presumably is also true
for the 755CX. Once you have the clocks list, you can put it in the
config file and forget it.
It's entirely possible that you can use a clocks list from another 755
model, so if you can't get a proper clocks list for your model, try
the list below.
There is no functional difference between the wd90c24 and the wd90c30,
which is why your 24 is identified as a 30. However, the driver is
unable to detect the difference between the wd90c24/wd90c30 and the
wd90c24a/wd90c31 -- and this _does_ matter, for performance reasons.
Force the use of the wd90c31 by an appropriate "chipset" declaration
in the config:
Section "Device"
Identifier "ThinkPad 755C Video"
VendorName "Western Digital"
BoardName "Unknown"
Chipset "wd90c31"
Clocks 25.17 28.32 64.99 35.99 25.18 28.36 65.05 35.99
Clocks 25.18 28.32 64.99 36.00 25.18 28.32 65.06 35.99
Clocks 44.28
VideoRam 1024
EndSection
Finally, there are at least two WWW pages for ThinkPads running Linux,
and you should check them out for any further hints. I seem to recall
that one of them addresses the issues involved with the 755CX video.
The first of these is a bit more complete than the second:
http://peipa.essex.ac.uk/tp-linux/tp-linux.html
http://www.hooked.net/people/jesse/linux/