XO-1 DCON trouble with new kernels

Daniel Drake dsd at laptop.org
Sat Nov 13 18:08:23 EST 2010


I'm hoping that someone can point me in the right direction, regarding
how the DCON works.

On new kernels, XO-1 DCON freeze doesn't work when you are on the
virtual terminal. The current display does not seem to get loaded into
the DCON memory, but then the freeze (video source switch) does
The DCON code has not changed between these kernel versions.

It still works OK when you are in X.

To illustrate more:
1. Boot up XO
2. Change to virtual terminal
3. echo 1 > /sys/devices/platform/dcon/freeze

You now see the image that OFW froze the screen with before booting Linux

4. echo 0 > /sys/devices/platform/dcon/freeze
Unfreeze works fine.

5. Go into X
6. echo 1 > /sys/devices/platform/dcon/freeze
Display freezes fine, with the X display contents
7. echo 0 > /sys/devices/platform/dcon/freeze
8. Go to virtual terminal
9. echo 1 > /sys/devices/platform/dcon/freeze
Display freezes fine, with the X display contents that were frozen in step 6

I have examined the steps taken between the working (X) and
non-working (VT) cases. They appear the same - after requesting the
switch, an interrupt arrives, and status is read back as 2 at that
time (switch to DCON mode complete).

Any idea what could be the cause of this?
For example, does the DCON only copy a certain region of video memory?
Perhaps Linux VT is now using a different region.

Or, any suggested diagnostics?


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