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powerpc/64: Optimise set/clear of CTRL[RUN] (runlatch)

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On modern CPUs the CTRL register is read-only except bit 63 which is
the run latch control. This means it can be updated with a mtspr
rather than mfspr/mtspr.

To accomodate older CPUs (Cell at least), where there are other bits
in the register, we still do a read/modify/write on pre 2.06 CPUs.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
[mpe: Update change log to mention 2.06 workaround]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2017-08-12 02:39:07 +10:00 committed by Michael Ellerman
parent 7b76a1f5ed
commit d1d0d5ffb3
1 changed files with 27 additions and 8 deletions
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35
arch/powerpc/kernel/process.c
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@ -1979,11 +1979,25 @@ void show_stack(struct task_struct *tsk, unsigned long *stack)
void notrace __ppc64_runlatch_on(void)
{
struct thread_info *ti = current_thread_info();
unsigned long ctrl;
ctrl = mfspr(SPRN_CTRLF);
ctrl |= CTRL_RUNLATCH;
mtspr(SPRN_CTRLT, ctrl);
if (cpu_has_feature(CPU_FTR_ARCH_206)) {
/*
* Least significant bit (RUN) is the only writable bit of
* the CTRL register, so we can avoid mfspr. 2.06 is not the
* earliest ISA where this is the case, but it's convenient.
*/
mtspr(SPRN_CTRLT, CTRL_RUNLATCH);
} else {
unsigned long ctrl;
/*
* Some architectures (e.g., Cell) have writable fields other
* than RUN, so do the read-modify-write.
*/
ctrl = mfspr(SPRN_CTRLF);
ctrl |= CTRL_RUNLATCH;
mtspr(SPRN_CTRLT, ctrl);
}
ti->local_flags |= _TLF_RUNLATCH;
}
@ -1992,13 +2006,18 @@ void notrace __ppc64_runlatch_on(void)
void notrace __ppc64_runlatch_off(void)
{
struct thread_info *ti = current_thread_info();
unsigned long ctrl;
ti->local_flags &= ~_TLF_RUNLATCH;
ctrl = mfspr(SPRN_CTRLF);
ctrl &= ~CTRL_RUNLATCH;
mtspr(SPRN_CTRLT, ctrl);
if (cpu_has_feature(CPU_FTR_ARCH_206)) {
mtspr(SPRN_CTRLT, 0);
} else {
unsigned long ctrl;
ctrl = mfspr(SPRN_CTRLF);
ctrl &= ~CTRL_RUNLATCH;
mtspr(SPRN_CTRLT, ctrl);
}
}
#endif /* CONFIG_PPC64 */