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Linux kernel with patched DSDT for Intel Classmate laptops. Fixes EC interrupt spew and delayed LID events.
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iSchool Linux Classmate Kernel

This patched DSDT fixes a problem with the DSDT supplied by the Intel Classmate laptop's BIOS, which interacts particularly badly with the Ubuntu Lucid kernel (2.6.32).


Lid open/closed events are long delayed. We've observed delays of several hours. It doesn't happen to all Classmates, it's usually repeatable on each one, but sometimes magically fixes itself.

When the lid is closed on a faulty Classmate, the backlight goes off, but the kernel doesn't generate any ACPI events (as shown by running acpi_listen or kacpimon) and the contents of /proc/acpi/button/lid/LID/state doesn't change, until several hours later.

Software versions

This has only been tested using Ubuntu Lucid (10.04 LTS) and the Linux 2.5.32-36 kernel. I think the problem exists in all older kernels, and potentially any later version if acpid is not running or the brightness keys (Fn+F7 and Fn+F8) are not configured or don't change the backlight level.

Description of the problem

The problem occurs when automatic brightness control is enabled by pressing Fn+F10. The embedded controller signals the kernel to execute the following control method in the DSDT:


which enables a timer in the EC (the LSST flag, I think) which then triggers every 10-30 ms, sending a message to the kernel to execute this control method:


That method is supposed to adjust the screen brightness to match the ambient light level, or something. It does this by simulating keypresses of the brightness up and down keys (Fn+F7 and Fn+F8) which send the kernel a Notify on the Fn key:

Notify (FNBT, 0x83)

(and 0x84, 0x93, 0x94), which is supposed to make the kernel increase or decrease the screen brightness. _Q2A does this in a loop with delays adding up to 120 ms times the difference in brightness level between the target and current level.

So if the kernel responds to these brightness change events, the first _Q2A will adjust the brightness to the desired levels, and the remaining ones will do nothing (except sleep for 10 ms) when invoked. Because the first invocation of _Q2A will take at least 120 ms, and these events are generated every 10-30 ms, there will be some queued up to execute while _Q2A runs for the first time. But the queue will eventually empty and other events can be processed.

The problem happens because the Lucid kernel doesn't respond to these brightness events. I think it doesn't even know about them. I think later kernels such as 3.4.7 do know about them, but generate an Input layer event (a kind of keypress) which acpid or X is supposed to receive and interpret to change the brightness.

In any case, until and unless the brightness ends up at the expected level, every invocation of _Q2A will take at least 120 ms, and as the events which trigger them are queued up every 10-30 ms, the queue grows and other events, particularly LID events, are long delayed (up to several hours, or four times as long as the system has been booted before the lid is closed).

Reproducing the problem

You can see this happening if you boot a kernel with ACPI and dynamic debugging enabled, i.e. the following kernel options:


Disable automatic brightness (e.g. using Fn+F7 to adjust brightness manually), enable some debugging messages:

mount -t debugfs none /sys/kernel/debug
echo '0x00000004' | tee /sys/module/acpi/parameters/debug_layer
echo '0x00000004' | tee /sys/module/acpi/parameters/debug_level
echo -n 'file ec.c +p' | tee /sys/kernel/debug/dynamic_debug/control
tail -f /var/log/syslog /var/log/debug | egrep '(push query execution|ev_queue_notify_reques)'

If you see any of these, then you didn't disable automatic brightness yet:

acpi:ACPI: EC: push query execution (0x2a) on queue

If you see a constant stream of these messages, then wait for it to finish (wait for the queue to empty; it may be faster to reboot as this can take several hours, up to 12 times as long as the system has been booted for):

evmisc-0125 [07] ev_queue_notify_reques: Dispatching Notify on [FNBT] Node f70152b8 Value 0x83 (**Device Specific**)
evmisc-0201 [07] ev_queue_notify_reques: No notify handler for Notify (FNBT, 83) node f70152b8

If you see nothing, try closing the lid and check that you see the following (if not, try to figure out where syslogd is sending messages from /proc/kmsg):

acpi:ACPI: EC: push query execution (0x19) on queue
evmisc-0125 [07] ev_queue_notify_reques: Dispatching Notify on [LID_] Node f7018060 Value 0x80 (**Device Specific**)

When you open the lid, you should see this message:

acpi:ACPI: EC: push query execution (0x16) on queue
evmisc-0125 [07] ev_queue_notify_reques: Dispatching Notify on [LID_] Node f7018060 Value 0x80 (**Device Specific**)

This means that the event from the enbedded controller (0x19 or 0x16) is quickly dispatched to the operating system (Notify on the LID_ device).

Now try enabling automatic brightness for 10 seconds (Fn+F10, wait 10 seconds, Fn+F7) and then close and open the lid. You should see that the Dispatching Notify on [FNBT] messages continue for about 30 seconds after you press Fn+F7, and the Dispatching Notify on [LID_] messages only appear after all of these have been processed, i.e. 30 seconds late.


The workaround in DSDT.asl is to disable the _Q13 control method which responds to Fn+F10 by enabling the timer; and if we receive any _Q2A events, which indicate that the timer is already enabled, then we disable it, so we should not get any more _Q2A events after that.

The supplied kernel.config enables the ACPI and dynamic debugging options listed earlier, and tells the kernel to override the DSDT using the supplied version. You can build this kernel by following these steps:

git clone git://
git clone git://
cp linux-ischool-classmate/kernel.config ubuntu-lucid/.config
cp linux-ischool-classmate/DSDT.hex ubuntu-lucid/
cd ubuntu-lucid/
CONCURRENCY_LEVEL=3 fakeroot make-kpkg --initrd \
    --append-to-version=-cw-custom-dsdt-120731-1 \
    kernel-image kernel-headers kernel-debug

Copy the resulting kernel package to a Classmate laptop and install it. Then run update-initramfs and update-grub:

sudo update-initramfs -k -c
sudo update-grub

Check that update-grub detects both the new kernel and its corresponding initrd.img, then reboot using the new kernel and verify that the problem is fixed.


  • DSDT.dsl is the source code for the modified DSDT with the fix.
  • DSDT.dsl.orig is the source code for the original, unmodified DSDT which does not compile due to errors in the code.
  • Makefile uses the Intel compiler iasl to compile DSDT.dsl into DSDT.hex and DSDT.aml.
  • DSDT.hex is the compiled C code to be inserted into the Linux kernel.
  • kernel.config is the Linux kernel configuration used to build the replacement kernel for the Intel Classmate as described above.
  • kernel.config-2.6.32-36-generic is the original kernel configuration on which the replacement is based.

Realtek RTL8192 driver DKMS package

Based on r8169 by Tista, updated to the latest 0007.0809.2012 driver release from Realtek.

See this thread for details of the problems with this card. Precise drivers don't work reliably.

To build the DKMS package:

git clone git://
cd linux-ischool-classmate/rtl8192ce-dkms/r8192ce-0007.0809.2012-1~classmate~121102~1cw
debuild -i -us -uc -b
dpkg -i ../r8192ce_0007.0809.2012-1~classmate~121102~1cw_all.deb
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