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| author | Nicholas Piggin <npiggin@gmail.com> | 2017-08-11 19:39:07 +0300 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-08-23 16:48:38 +0300 |
| commit | d1d0d5ffb3006eaf9b5f41c89fe801e032cbbfe4 (patch) | |
| tree | cfb1d7cec1dc0e7e3382efc64a2beb54f041799d /arch/powerpc/kernel/process.c | |
| parent | 7b76a1f5ed9c7233cfdd35b6f77310ccec293921 (diff) | |
| download | linux-d1d0d5ffb3006eaf9b5f41c89fe801e032cbbfe4.tar.xz | |
powerpc/64: Optimise set/clear of CTRL[RUN] (runlatch)
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>
Diffstat (limited to 'arch/powerpc/kernel/process.c')
| -rw-r--r-- | arch/powerpc/kernel/process.c | 35 |
1 files changed, 27 insertions, 8 deletions
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 34bd94b090e2..0a00d59df537 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -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 */ |