cpu: Introduce smt_lowest()

Recent CPUs have introduced a lower SMT priority. This uses the
Linux pattern of executing priority nops in descending order to
get a simple portable way to put the CPU into lowest SMT priority.

Introduce smt_lowest() and use it in place of smt_very_low and
smt_low ; smt_very_low sequences.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>

asm/head.S

@@ -398,7 +398,7 @@ secondary_wait:
 	 */
 	LOAD_IMM32(%r3, boot_flag - __head)
 	add	%r3,%r3,%r30
-1:	smt_very_low
+1:	smt_lowest
 	lwz	%r0,0(%r3)
 	cmpdi	%r0,0
 	beq	1b
@@ -416,7 +416,7 @@ secondary_wait:
 1:
 	/* Now wait for cpu_secondary_start to be set */
 	LOAD_ADDR_FROM_TOC(%r3, cpu_secondary_start)
-1:	smt_very_low
+1:	smt_lowest
 	ld	%r0,0(%r3)
 	cmpdi	%r0,0
 	beq	1b
@@ -441,7 +441,7 @@ secondary_wait:
 
 	/* Not found... what to do ? set some global error ? */
 secondary_not_found:
-	smt_very_low
+	smt_lowest
 	b	.
 
 call_relocate:

core/cpu.c

@@ -871,7 +871,7 @@ void cpu_bringup(void)
 
 		/* Add a callin timeout ?  If so, call cpu_remove_node(t). */
 		while (t->state != cpu_state_active) {
-			smt_very_low();
+			smt_lowest();
 			sync();
 		}
 		smt_medium();

core/fast-reboot.c

@@ -488,7 +488,7 @@ void __noreturn fast_reboot_entry(void)
 	if (this_cpu() != boot_cpu) {
 		this_cpu()->state = cpu_state_present;
 		while (!fast_boot_release) {
-			smt_very_low();
+			smt_lowest();
 			sync();
 		}
 		smt_medium();
@@ -511,7 +511,7 @@ void __noreturn fast_reboot_entry(void)
 
 		/* XXX Add a callin timeout ? */
 		while (cpu->state != cpu_state_present) {
-			smt_very_low();
+			smt_lowest();
 			sync();
 		}
 		smt_medium();
@@ -534,7 +534,7 @@ void __noreturn fast_reboot_entry(void)
 
 		/* XXX Add a callin timeout ? */
 		while (cpu->state == cpu_state_present) {
-			smt_very_low();
+			smt_lowest();
 			sync();
 		}
 	}

include/cpu.h

@@ -121,8 +121,7 @@ extern struct cpu_thread *boot_cpu;
 static inline void __nomcount cpu_relax(void)
 {
 	/* Relax a bit to give sibling threads some breathing space */
-	smt_low();
-	smt_very_low();
+	smt_lowest();
 	asm volatile("nop; nop; nop; nop;\n"
 		     "nop; nop; nop; nop;\n"
 		     "nop; nop; nop; nop;\n"

include/processor.h

@@ -197,6 +197,7 @@
 #define smt_medium_low	or 6,6,6
 #define smt_extra_high	or 7,7,7
 #define smt_very_low	or 31,31,31
+#define smt_lowest	smt_low ; smt_very_low
 
 #else /* __ASSEMBLY__ */
 
@@ -214,6 +215,7 @@ static inline void smt_medium_high(void){ asm volatile("or 5,5,5");	}
 static inline void smt_medium_low(void)	{ asm volatile("or 6,6,6");	}
 static inline void smt_extra_high(void)	{ asm volatile("or 7,7,7");	}
 static inline void smt_very_low(void)	{ asm volatile("or 31,31,31");	}
+static inline void smt_lowest(void)	{ smt_low(); smt_very_low();	}
 
 /*
  * SPR access functions