powerpc/powernv/idle: Use Requested Level for restoring state on P9 DD1

On Power9 DD1 due to a hardware bug the Power-Saving Level Status
field (PLS) of the PSSCR for a thread waking up from a deep state can
under-report if some other thread in the core is in a shallow stop
state. The scenario in which this can manifest is as follows:

   1) All the threads of the core are in deep stop.
   2) One of the threads is woken up. The PLS for this thread will
      correctly reflect that it is waking up from deep stop.
   3) The thread that has woken up now executes a shallow stop.
   4) When some other thread in the core is woken, its PLS will reflect
      the shallow stop state.

Thus, the subsequent thread for which the PLS is under-reporting the
wakeup state will not restore the hypervisor resources.

Hence, on DD1 systems, use the Requested Level (RL) field as a
workaround to restore the contents of the hypervisor resources on the
wakeup from the stop state.
Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/paca.h

@@ -177,6 +177,8 @@ struct paca_struct {
 	 * to the sibling threads' paca.
 	 */
 	struct paca_struct **thread_sibling_pacas;
+	/* The PSSCR value that the kernel requested before going to stop */
+	u64 requested_psscr;
 #endif
 
 #ifdef CONFIG_PPC_STD_MMU_64

arch/powerpc/kernel/asm-offsets.c

@@ -742,6 +742,7 @@ int main(void)
 	OFFSET(PACA_THREAD_MASK, paca_struct, thread_mask);
 	OFFSET(PACA_SUBCORE_SIBLING_MASK, paca_struct, subcore_sibling_mask);
 	OFFSET(PACA_SIBLING_PACA_PTRS, paca_struct, thread_sibling_pacas);
+	OFFSET(PACA_REQ_PSSCR, paca_struct, requested_psscr);
 #endif
 
 	DEFINE(PPC_DBELL_SERVER, PPC_DBELL_SERVER);

arch/powerpc/kernel/idle_book3s.S

@@ -379,6 +379,7 @@ _GLOBAL(power9_idle_stop)
 	mfspr   r5,SPRN_PSSCR
 	andc    r5,r5,r4
 	or      r3,r3,r5
+	std	r3, PACA_REQ_PSSCR(r13)
 	mtspr 	SPRN_PSSCR,r3
 	LOAD_REG_ADDR(r5,power_enter_stop)
 	li	r4,1
@@ -498,12 +499,22 @@ pnv_restore_hyp_resource_arch300:
 	LOAD_REG_ADDRBASE(r5,pnv_first_deep_stop_state)
 	ld	r4,ADDROFF(pnv_first_deep_stop_state)(r5)
 
-	mfspr	r5,SPRN_PSSCR
+BEGIN_FTR_SECTION_NESTED(71)
+	/*
+	 * Assume that we are waking up from the state
+	 * same as the Requested Level (RL) in the PSSCR
+	 * which are Bits 60-63
+	 */
+	ld	r5,PACA_REQ_PSSCR(r13)
+	rldicl  r5,r5,0,60
+FTR_SECTION_ELSE_NESTED(71)
 	/*
 	 * 0-3 bits correspond to Power-Saving Level Status
 	 * which indicates the idle state we are waking up from
 	 */
+	mfspr	r5, SPRN_PSSCR
 	rldicl  r5,r5,4,60
+ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_POWER9_DD1, 71)
 	cmpd	cr4,r5,r4
 	bge	cr4,pnv_wakeup_tb_loss /* returns to caller */