Re: [PATCH 18/18] powerpc/64s: move power4 idle entirely to C

[Christophe Leroy]

Le 05/11/2020 à 15:34, Nicholas Piggin a écrit :

Christophe asked about doing this, most of the code is still in
asm but maybe it's slightly nicer? I don't know if it's worthwhile.

Heu... I don't think I was asking for that, but why not, see later comments.

At first I was just asking to write the following in C:

+
+       .globl power4_idle_nap_return
+power4_idle_nap_return:
+       blr


In extenso, instead of the above do somewhere something like:

void power4_idle_nap_return(void)
{
}

---
  arch/powerpc/kernel/idle.c        | 25 ++++++++++++++++++++-----
  arch/powerpc/kernel/idle_book3s.S | 22 ----------------------
  2 files changed, 20 insertions(+), 27 deletions(-)

diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index ae0e2632393d..849e77a45915 100644
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -72,6 +72,9 @@ int powersave_nap;
  #ifdef CONFIG_PPC_970_NAP
  void power4_idle(void)
  {
+       unsigned long msr_idle = MSR_KERNEL|MSR_EE|MSR_POW;
+       unsigned long tmp1, tmp2;
+
        if (!cpu_has_feature(CPU_FTR_CAN_NAP))
                return;

@@ -84,13 +87,25 @@ void power4_idle(void)

        if (cpu_has_feature(CPU_FTR_ALTIVEC))
                asm volatile("DSSALL ; sync" ::: "memory");

- power4_idle_nap();

-
+       asm volatile(
+" ld      %0,PACA_THREAD_INFO(r13)                \n"
+" ld      %1,TI_LOCAL_FLAGS(%0)                   \n"
+" ori     %1,%1,_TLF_NAPPING                      \n"
+" std     %1,TI_LOCAL_FLAGS(%0)                   \n"

Can't this just be:

        current_thread_info()->local_flags |= _TLF_NAPPING;

        /*
-        * power4_idle_nap returns with interrupts enabled (soft and hard).
-        * to our caller with interrupts enabled (soft and hard). Our caller
-        * can cope with either interrupts disabled or enabled upon return.
+        * NAPPING bit is set, from this point onward nap_adjust_return()
+        * will cause interrupts to return to power4_idle_nap_return.
         */
+"1:       sync                                            \n"
+" isync                                           \n"
+" mtmsrd  %2                                      \n"
+" isync                                           \n"
+" b       1b                                      \n"

And this:

        for (;;) {
                mb();
                isync();
                mtmsr(MSR_KERNEL|MSR_EE|MSR_POW);
                isync();
        }

+" .globl power4_idle_nap_return                   \n"
+"power4_idle_nap_return:                          \n"
+       : "=r"(tmp1), "=r"(tmp2)
+       : "r"(msr_idle)
+       );
  }
  #endif

Christophe