3 files changed, 57 insertions, 14 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 15f79c27748d..0f5c3b4347c6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -866,6 +866,15 @@
 
         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 aware of.
+
         dump_apple_properties   [X86]
                         Dump name and content of EFI device properties on
                         x86 Macs.  Useful for driver authors to determine
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index f7c8f9972f61..4a4a05afcaf7 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -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
diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index fcc7588a96d6..76eebba13a1d 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -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>
@@ -671,12 +672,24 @@ 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)
 {
@@ -707,7 +720,7 @@ 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);
@@ -756,6 +769,26 @@ 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)
 {
@@ -766,8 +799,6 @@ 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;
@@ -775,6 +806,8 @@ 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;
@@ -782,6 +815,9 @@ 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;
@@ -1027,5 +1063,8 @@ 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);
 }