reset on mpc83xx

Rasmus Villemoes rasmus.villemoes at
Thu Apr 30 16:44:19 CEST 2020


I'm wondering why the sysreset_mpc83xx driver (as well as the similar
code in arch/powerpc/cpu/mpc83xx/cpu.c) removes the MSR_IR and MSR_DR
bits from MSR.

On my mpc8309, that seems to simply make the board hang right after
writing the new MSR value - i.e., it never gets to write the magic value
0x52535445 to RPR and of course not to then actually do the reset.

-       msr &= ~(MSR_EE | MSR_IR | MSR_DR);
+       msr &= ~(MSR_EE);

(whether using the sysreset driver or the cpu.c code) makes the board
reset as expected.

The linux kernel's mpc83xx_restart() doesn't seem to remove those bits,
and rebooting from linux works as expected - it does local_irq_disable()
which amounts to clearing the EE bit.

But since the arch/powerpc/cpu/mpc83xx/cpu.c code in U-Boot has been
there forever, I assume I'm missing something fundamental.

[The board happens to have an external watchdog circuit that performs a
power cycle after a while, but there are cases, e.g. bootstrapping,
where that circuitry is disabled, and moreover, we'd like to be able to
make use of the reset status register to distinguish a reset from a cold


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