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>
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 34bd94b..0a00d59 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 */
