Hi,
-------- Original-Nachricht --------
> Datum: Fri, 22 Feb 2008 11:24:38 -0600
> Von: Milton Miller <[EMAIL PROTECTED]>
> An: Gerhard Pircher <[EMAIL PROTECTED]>
> CC: ppcdev <linuxppc-dev@ozlabs.org>
> Betreff: Re: How to dynamically disable/enable CPU features?
> We handle cpu features in a couple of ways:
> (1) we replace assembly instructions with nop early in the kernel boot
I'm pretty sure that is the problem.
> (2) we test the feature flags in c code
>
> In (2), we form two expressions for features that are
> (a) always set
> (b) never set
> so that the compiler can eliminate the test based on the config.
>
> To change a flag, you must make sure its in POSSIBLE but not ALWAYS,
> and also set it before it is used, either to nop out instructions (see
> early_init in setup-32.c for 32 bit), or tested by c code (in this
> case, maybe the initial_mmu setup is testing NEED_COHERENT, which is
> between early_init and probe). The code path is a bit different for 64
> bit.
The flag is in POSSIBLE. I now use this code in the platform probe
function to nop out the code affected by the flag:
cur_cpu_spec->cpu_features &= ~CPU_FTR_NEED_COHERENT;
/* Patch out unwanted feature. */
do_feature_fixups(cur_cpu_spec->cpu_features,
PTRRELOC(&__start___ftr_fixup),
PTRRELOC(&__stop___ftr_fixup));
It seems to work so far, but I would like to know if this is the right
way to do it, or if calling do_feature_fixups() more than once can have
any side effects.
regards,
Gerhard
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