[PATCH 09/13] powerpc/64: runlatch CTRL[RUN] set optimisation
From: Nicholas Piggin <npiggin@gmail.com>
Date: 2017-08-05 17:03:25
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Linus Torvalds
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. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> --- arch/powerpc/kernel/process.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-)
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 9f3e2c932dcc..75306b6e1812 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c@@ -1994,11 +1994,25 @@ 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; }
@@ -2007,13 +2021,18 @@ 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 */
--
2.11.0