[PATCH v2] powerpc/64s: Add dt_cpu_ftrs boot time setup option

@@ -866,6 +866,16 @@
 
 	dscc4.setup=	[NET]
 
+	dt_cpu_ftrs=	[PPC]
+			Format: {"off" | "known"}
+			Control how the dt_cpu_ftrs device-tree binding is
+			used for CPU feature discovery and setup (if it
+			exists).
+			off: Do not use it, fall back to legacy cpu table.
+			known: Do not pass through unknown features to guests
+			or userspace, only those that the kernel is not aware
+			of.
+
 	dump_apple_properties	[X86]
 			Dump name and content of EFI device properties on
 			x86 Macs.  Useful for driver authors to determine

@@ -391,11 +391,6 @@ config PPC_DT_CPU_FTRS
 	  firmware provides this binding.
 	  If you're not sure say Y.
 
-config PPC_CPUFEATURES_ENABLE_UNKNOWN
-	bool "cpufeatures pass through unknown features to guest/userspace"
-	depends on PPC_DT_CPU_FTRS
-	default y
-
 config HIGHMEM
 	bool "High memory support"
 	depends on PPC32

@@ -8,6 +8,7 @@
 #include <linux/export.h>
 #include <linux/init.h>
 #include <linux/jump_label.h>
+#include <linux/libfdt.h>
 #include <linux/memblock.h>
 #include <linux/printk.h>
 #include <linux/sched.h>

@@ -670,12 +671,24 @@ static struct dt_cpu_feature_match __initdata
 	{"wait-v3", feat_enable, 0},
 };
 
-/* XXX: how to configure this? Default + boot time? */
-#ifdef CONFIG_PPC_CPUFEATURES_ENABLE_UNKNOWN
-#define CPU_FEATURE_ENABLE_UNKNOWN 1
-#else
-#define CPU_FEATURE_ENABLE_UNKNOWN 0
-#endif
+static bool __initdata using_dt_cpu_ftrs;
+static bool __initdata enable_unknown = true;
+
+static int __init dt_cpu_ftrs_parse(char *str)
+{
+	if (!str)
+		return 0;
+
+	if (!strcmp(str, "off"))
+		using_dt_cpu_ftrs = false;
+	else if (!strcmp(str, "known"))
+		enable_unknown = false;
+	else
+		return 1;
+
+	return 0;
+}
+early_param("dt_cpu_ftrs", dt_cpu_ftrs_parse);
 
 static void __init cpufeatures_setup_start(u32 isa)
 {

@@ -706,7 +719,7 @@ static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
 		}
 	}
 
-	if (!known && CPU_FEATURE_ENABLE_UNKNOWN) {
+	if (!known && enable_unknown) {
 		if (!feat_try_enable_unknown(f)) {
 			pr_info("not enabling: %s (unknown and unsupported by kernel)\n",
 				f->name);

@@ -755,6 +768,26 @@ static void __init cpufeatures_setup_finished(void)
 		cur_cpu_spec->cpu_features, cur_cpu_spec->mmu_features);
 }
 
+static int __init disabled_on_cmdline(void)
+{
+	unsigned long root, chosen;
+	const char *p;
+
+	root = of_get_flat_dt_root();
+	chosen = of_get_flat_dt_subnode_by_name(root, "chosen");
+	if (chosen == -FDT_ERR_NOTFOUND)
+		return false;
+
+	p = of_get_flat_dt_prop(chosen, "bootargs", NULL);
+	if (!p)
+		return false;
+
+	if (strstr(p, "dt_cpu_ftrs=off"))
+		return true;
+
+	return false;
+}
+
 static int __init fdt_find_cpu_features(unsigned long node, const char *uname,
 					int depth, void *data)
 {

@@ -765,8 +798,6 @@ static int __init fdt_find_cpu_features(unsigned long node, const char *uname,
 	return 0;
 }
 
-static bool __initdata using_dt_cpu_ftrs = false;
-
 bool __init dt_cpu_ftrs_in_use(void)
 {
 	return using_dt_cpu_ftrs;

@@ -774,6 +805,8 @@ bool __init dt_cpu_ftrs_in_use(void)
 
 bool __init dt_cpu_ftrs_init(void *fdt)
 {
+	using_dt_cpu_ftrs = false;
+
 	/* Setup and verify the FDT, if it fails we just bail */
 	if (!early_init_dt_verify(fdt))
 		return false;

@@ -781,6 +814,9 @@ bool __init dt_cpu_ftrs_init(void *fdt)
 	if (!of_scan_flat_dt(fdt_find_cpu_features, NULL))
 		return false;
 
+	if (disabled_on_cmdline())
+		return false;
+
 	cpufeatures_setup_cpu();
 
 	using_dt_cpu_ftrs = true;

@@ -1026,5 +1062,8 @@ static int __init dt_cpu_ftrs_scan_callback(unsigned long node, const char
 
 void __init dt_cpu_ftrs_scan(void)
 {
+	if (!using_dt_cpu_ftrs)
+		return;
+
 	of_scan_flat_dt(dt_cpu_ftrs_scan_callback, NULL);
 }