Nicholas Piggin <npig...@gmail.com> writes:
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index baae104b16c7..f587c1fdf981 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1960,11 +1960,25 @@ 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);
> + }
Does the generated code look any good if you do something like:
unsigned long ctrl;
ctrl = 0;
if (!cpu_has_feature(CPU_FTR_ARCH_206))
ctrl = mfspr(SPRN_CTRLF);
ctrl |= CTRL_RUNLATCH;
mtspr(SPRN_CTRLT, ctrl);
That would offend me slightly less ;)
cheers
