ibook2r2 & strange freeze.

Brice Figureau brice at tincell.com
Sun Apr 27 06:51:43 EST 2003

On Saturday, April 26, 2003, at 10:35 PM, Benjamin Herrenschmidt wrote:
> On Sat, 2003-04-26 at 22:22, Brice Figureau wrote:
>> On Saturday, April 26, 2003, at 12:33 PM, Benjamin Herrenschmidt
>> wrote:
>>>> After several hours of kernel compiling (my ibook is not that fast
>>>> ;-)), I found that the latest working patch is -ben8.
>>>> The first non working is then -ben9.
>>> Great, many thanks. That will help.
>>> Can you try now to put drivers/video/radeonfb.c from -ben8 into
>>> -ben9 (and then -ben10 if it works) and tell me if that helps ?
>> Here is the results:
>>   -ben9 with -ben8 radeon crashes exactly at the same place
>>   -ben10 with -ben8 radeon crashes exacctly like -ben9
> That's weird since you say using no video driver (that is offb) seems
> to cure the problem and the backtrace tend to show an fbcon problem,
> but there is nothing different in the fbcon layer afaik.
The pc was in fbcon_radeon_bmove, so even if it's a fbcon problem, the
crash is happening into the radeonfb module...
video=ofonly works fine because it does not use fbcon_radeon_bmove I

> So there is probably some memory corruption going on... I'm comparing
> other bits of ben8 and ben9 now and see nothing relevants. The changes
> where in the cache flush affecting cpufreq and sleep, and radeonfb...
Since the crash occurs in the scoll, if there is a problem with the
font (corrupted font or something) the scroll computation might be
wrong, and thus fbcon_radeon_bmove might copy some memory from/to a bad

>> Just to remind you:
>>   -ben9 crashes always at the same place (and triggers xmon, have a
>> look
>> at the backtrace)
>>   -ben10 freezes randomly, usually in the boot process. It freezes
>> often
>> right after the font uploading to the console layer, but sometimes
>> farther (I once could go until the network started). When it freezes
>> the last line at the bottom of the screen is printed *twice* (which
>> might confirm the -ben9 backtrace).
>> All the tested kernels were configured with CONFIG_PPC_RTC enabled
>> (and
>> CONFIG_RTC disabled), and CONFIG_CPU_FREQ disabled too.
>> noaccel parameters didn't seem to change anything. I might have to
>> check again.
> Just in case, the proper syntax in yaboot.conf is:
> append="video=radeon:noaccel"
Yes I know, it was just shorter to write noaccel in my mail ;-)

> The backtrace seem to indicate something wrong with fbcon_scroll,
> though
> I fail to see what/why, I suspect something else is causing it to die.

> With xmon, can you do:
> di %pc
> and then
> r
> So I can have a better idea of what it's doing. It's probably using
> a pointer that got overwritten, but the actual cause of the corruption
> can be completely elsewhere in the kernel. It may also be present in
> earlier kernels and happen to corrupt some other harmless bit of memory
> in them... Unfortunately, this one may be difficult to track down.
Unfortunately those bugs are the most difficult to find and fix.
What I could do is disable some part of the -ben9 patch in favor of the
-ben8 version, until I find in which part it happens.

I'll let you know what I found.


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