powerpc/book3e: Add generic 64-bit idle powersave support

We use a similar technique to ppc32: We set a thread local flag
to indicate that we are about to enter or have entered the stop
state, and have fixup code in the async interrupt entry code that
reacts to this flag to make us return to a different location
(sets NIP to LINK in our case).

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
--
v2. Fix lockdep bug
    Re-mask interrupts when coming back from idle

1 files changed, 23 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/exceptions-64e.S b/arch/powerpc/kernel/exceptions-64e.S
index a42637c3a72d..316465a32a9c 100644
--- a/arch/powerpc/kernel/exceptions-64e.S
+++ b/arch/powerpc/kernel/exceptions-64e.S
@@ -204,11 +204,30 @@ exc_##n##_bad_stack:							    \
         lis     r,TSR_FIS@h;                                            \
         mtspr   SPRN_TSR,r
 
+/* Used by asynchronous interrupt that may happen in the idle loop.
+ *
+ * This check if the thread was in the idle loop, and if yes, returns
+ * to the caller rather than the PC. This is to avoid a race if
+ * interrupts happen before the wait instruction.
+ */
+#define CHECK_NAPPING()                                                 \
+        clrrdi  r11,r1,THREAD_SHIFT;                                    \
+        ld      r10,TI_LOCAL_FLAGS(r11);                                \
+        andi.   r9,r10,_TLF_NAPPING;                                    \
+        beq+    1f;                                                     \
+        ld      r8,_LINK(r1);                                           \
+        rlwinm  r7,r10,0,~_TLF_NAPPING;                                 \
+        std     r8,_NIP(r1);                                            \
+        std     r7,TI_LOCAL_FLAGS(r11);                                 \
+1:
+
+
 #define MASKABLE_EXCEPTION(trapnum, label, hdlr, ack)                   \
         START_EXCEPTION(label);                                         \
         NORMAL_EXCEPTION_PROLOG(trapnum, PROLOG_ADDITION_MASKABLE)      \
         EXCEPTION_COMMON(trapnum, PACA_EXGEN, INTS_DISABLE_ALL)         \
         ack(r8);                                                        \
+        CHECK_NAPPING();                                                \
         addi    r3,r1,STACK_FRAME_OVERHEAD;                             \
         bl      hdlr;                                                   \
         b       .ret_from_except_lite;
@@ -257,6 +276,7 @@ interrupt_end_book3e:
         CRIT_EXCEPTION_PROLOG(0x100, PROLOG_ADDITION_NONE)
 //      EXCEPTION_COMMON(0x100, PACA_EXCRIT, INTS_DISABLE_ALL)
 //      bl      special_reg_save_crit
+//      CHECK_NAPPING();
 //      addi    r3,r1,STACK_FRAME_OVERHEAD
 //      bl      .critical_exception
 //      b       ret_from_crit_except
@@ -268,6 +288,7 @@ interrupt_end_book3e:
 //      EXCEPTION_COMMON(0x200, PACA_EXMC, INTS_DISABLE_ALL)
 //      bl      special_reg_save_mc
 //      addi    r3,r1,STACK_FRAME_OVERHEAD
+//      CHECK_NAPPING();
 //      bl      .machine_check_exception
 //      b       ret_from_mc_except
         b       .
@@ -338,6 +359,7 @@ interrupt_end_book3e:
         CRIT_EXCEPTION_PROLOG(0x9f0, PROLOG_ADDITION_NONE)
 //      EXCEPTION_COMMON(0x9f0, PACA_EXCRIT, INTS_DISABLE_ALL)
 //      bl      special_reg_save_crit
+//      CHECK_NAPPING();
 //      addi    r3,r1,STACK_FRAME_OVERHEAD
 //      bl      .unknown_exception
 //      b       ret_from_crit_except
@@ -434,6 +456,7 @@ kernel_dbg_exc:
         CRIT_EXCEPTION_PROLOG(0x2080, PROLOG_ADDITION_NONE)
 //      EXCEPTION_COMMON(0x2080, PACA_EXCRIT, INTS_DISABLE_ALL)
 //      bl      special_reg_save_crit
+//      CHECK_NAPPING();
 //      addi    r3,r1,STACK_FRAME_OVERHEAD
 //      bl      .doorbell_critical_exception
 //      b       ret_from_crit_except