powerpc: Correct smt_enabled=X boot option for > 2 threads per core

The 'smt_enabled=X' boot option does not handle values of X > 2.
For Power 7 processors with smt modes of 0,1,2,3, and 4 this does
not work. This patch allows the smt_enabled option to be set to
any value limited to a max equal to the number of threads per
core.

Signed-off-by: Nathan Fontenot <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/kernel/setup_64.c

···
 
 #ifdef CONFIG_SMP
 
-static int smt_enabled_cmdline;
+static char *smt_enabled_cmdline;
 
 /* Look for ibm,smt-enabled OF option */
 static void check_smt_enabled(void)
···
 	struct device_node *dn;
 	const char *smt_option;
 
+	/* Default to enabling all threads */
+	smt_enabled_at_boot = threads_per_core;
+
 	/* Allow the command line to overrule the OF option */
-	if (smt_enabled_cmdline)
-		return;
+	if (smt_enabled_cmdline) {
+		if (!strcmp(smt_enabled_cmdline, "on"))
+			smt_enabled_at_boot = threads_per_core;
+		else if (!strcmp(smt_enabled_cmdline, "off"))
+			smt_enabled_at_boot = 0;
+		else {
+			long smt;
+			int rc;
 
-	dn = of_find_node_by_path("/options");
+			rc = strict_strtol(smt_enabled_cmdline, 10, &smt);
+			if (!rc)
+				smt_enabled_at_boot =
+					min(threads_per_core, (int)smt);
+		}
+	} else {
+		dn = of_find_node_by_path("/options");
+		if (dn) {
+			smt_option = of_get_property(dn, "ibm,smt-enabled",
+						     NULL);
 
-	if (dn) {
-		smt_option = of_get_property(dn, "ibm,smt-enabled", NULL);
+			if (smt_option) {
+				if (!strcmp(smt_option, "on"))
+					smt_enabled_at_boot = threads_per_core;
+				else if (!strcmp(smt_option, "off"))
+					smt_enabled_at_boot = 0;
+			}
 
-                if (smt_option) {
-			if (!strcmp(smt_option, "on"))
-				smt_enabled_at_boot = 1;
-			else if (!strcmp(smt_option, "off"))
-				smt_enabled_at_boot = 0;
-                }
-        }
+			of_node_put(dn);
+		}
+	}
 }
 
 /* Look for smt-enabled= cmdline option */
 static int __init early_smt_enabled(char *p)
 {
-	smt_enabled_cmdline = 1;
-
-	if (!p)
-		return 0;
-
-	if (!strcmp(p, "on") || !strcmp(p, "1"))
-		smt_enabled_at_boot = 1;
-	else if (!strcmp(p, "off") || !strcmp(p, "0"))
-		smt_enabled_at_boot = 0;
-
+	smt_enabled_cmdline = p;
 	return 0;
 }
 early_param("smt-enabled", early_smt_enabled);
···
 	 */
 	xmon_setup();
 
-	check_smt_enabled();
 	smp_setup_cpu_maps();
+	check_smt_enabled();
 
 #ifdef CONFIG_SMP
 	/* Release secondary cpus out of their spinloops at 0x60 now that

arch/powerpc/platforms/pseries/smp.c

···
 	/* Special case - we inhibit secondary thread startup
 	 * during boot if the user requests it.
 	 */
-	if (system_state < SYSTEM_RUNNING &&
-	    cpu_has_feature(CPU_FTR_SMT) &&
-	    !smt_enabled_at_boot && cpu_thread_in_core(nr) != 0)
-		return 0;
+	if (system_state < SYSTEM_RUNNING && cpu_has_feature(CPU_FTR_SMT)) {
+		if (!smt_enabled_at_boot && cpu_thread_in_core(nr) != 0)
+			return 0;
+		if (smt_enabled_at_boot
+		    && cpu_thread_in_core(nr) >= smt_enabled_at_boot)
+			return 0;
+	}
 
 	return 1;
 }