new kernel ... / meaning of stable-tracking

andrzej zaborowski balrogg at
Wed Oct 1 20:16:39 CEST 2008

2008/10/1 Werner Almesberger <werner at>:
> andrzej zaborowski wrote:
>> First was when I was booting off the sd for the first time and the sd
>> had errors so the kernel loaded from nand okay and then init loaded
>> but then subsequent programs or scripts loaded corrupt and something
>> locked up, so I used the power button.
> Hmm, and then you booted from NAND and went on to repair the uSD card
> using the system booted from NAND ? Thanks, that's indeed a case where
> there's a visible difference, because we wouldn't even reach the point
> where neodog is running, yet the kernel isn't completely dead yet.
>> Second time was when I was hacking the timers yesterday and apparently
>> I broke gettimeofday and one of the first processes hung waiting for
>> something, I used the power button (for kicks) and it worked. (99% of
>> the times I was just taking the battery out and wouldn't mind doing it
>> that time also)
> You're very brave to do this kind of low-level hacking without a debug
> board ;-)
> By the way, my solution for quickly resetting the Neo without too much
> physical effort is to just toggle the debug board reset:
> I almost always keep the debug board attached, since I don't want to
> miss any clues printed on the serial console, and I also like to copy
> and paste printks for later reference (which I couldn't do if I only
> had them on the screen).

Yeah, that's a good thing.
I did get the debug board but I don't use it unless there's something
interesting happening before glamo initialises because flashing
kernels through u-boot seems quicker and for that I have to disconnect
the debug board everytime.

>> Something to consider is that Linux has something called SysRq key for
>> like 15 years and it's a similar concept.  It's something that works
>> at all times even after the kernel panicked and nobody doubts its
>> usefulness.
> Yes, SysRq is pretty close to this. Even there, the low-level driver
> only provides the SysRq keycode, but it's higher-level code that
> decides what to do with it. But I take your point that this is still
> in the kernel, not in user space.
> How about the following compromise: we leave the power-down code in
> the kernel, but move it from the interrupt handler to a separate
> function (perhaps in a separate file as well) that just gets called
> on ONKEY/SECOND events and that's responsible for handling
> onkey_seconds and perhaps also PCF50633_F_PWR_PRESSED.

Yes, sounds good, and also I'm not suggesting that it be forced
upstream.  I was just thinking if the SysRq mechanism couldn't be
reused by registering a tty etc, but it doesn't seem it could easily.


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