Re: Kernel panic on 2.4.22 (no TSC) when compiled for i486

[Mikael Pettersson]

Chris Sykes writes:
 > I'm getting a kernel panic from my 2.4.22 kernel when compiled for
 > i486 (see attached .config).
 > 
 > "Kernel panic: Kernel compiled for Pentium+, requires TSC feature!"
 > 
 > The CPU is a Cyrix Cx486DX2 100MHz part.  I tried booting with notsc
 > but I get the message:
 > "notsc: Kernel compiled with CONFIG_X86_TSC, cannot disable TSC."
 > 
 > The kernel will work fine when recompiled for i386.
 > 
 > Does a real 486 have a TSC, or is this a config bug?
...
 > CONFIG_M486=y
...
 > CONFIG_X86_TSC=y

I've reproduced this problem. It's a bug in the configuration
system which triggers when you change an option which has
derived options.

In this case, when first configuring for a CPU with TSC the
derived CONFIG_X86_TSC option is added. Then when reconfiguring
for a TSC-less CPU (e.g., 486) the derived option stays because
it derived from something that _was_ defined at the start of the
config run.

The workaround is to do an additional 'make oldconfig', after
which the derived option will be gone.

/Mikael
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