ARM: 6207/1: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and check for it on V6

The TLS register is only available on ARM1136 r1p0 and later.
Set HWCAP_TLS flags if hardware TLS is available and test for
it if CONFIG_CPU_32v6K is not set for V6.

Note that we set the TLS instruction in __kuser_get_tls
dynamically as suggested by Jamie Lokier <jamie@shareable.org>.

Also the __switch_to code is optimized out in most cases as
suggested by Nicolas Pitre <nico@fluxnic.net>.

Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

8 files changed, 105 insertions, 41 deletions

diff --git a/arch/arm/include/asm/hwcap.h b/arch/arm/include/asm/hwcap.h
index f7bd52b1c365..c1062c317103 100644
--- a/arch/arm/include/asm/hwcap.h
+++ b/arch/arm/include/asm/hwcap.h
@@ -19,6 +19,7 @@
 #define HWCAP_NEON      4096
 #define HWCAP_VFPv3     8192
 #define HWCAP_VFPv3D16  16384
+#define HWCAP_TLS       32768
 
 #if defined(__KERNEL__) && !defined(__ASSEMBLY__)
 /*
diff --git a/arch/arm/include/asm/tls.h b/arch/arm/include/asm/tls.h
new file mode 100644
index 000000000000..e71d6ff8d104
--- /dev/null
+++ b/arch/arm/include/asm/tls.h
@@ -0,0 +1,46 @@
+#ifndef __ASMARM_TLS_H
+#define __ASMARM_TLS_H
+
+#ifdef __ASSEMBLY__
+        .macro set_tls_none, tp, tmp1, tmp2
+        .endm
+
+        .macro set_tls_v6k, tp, tmp1, tmp2
+        mcr     p15, 0, \tp, c13, c0, 3         @ set TLS register
+        .endm
+
+        .macro set_tls_v6, tp, tmp1, tmp2
+        ldr     \tmp1, =elf_hwcap
+        ldr     \tmp1, [\tmp1, #0]
+        mov     \tmp2, #0xffff0fff
+        tst     \tmp1, #HWCAP_TLS               @ hardware TLS available?
+        mcrne   p15, 0, \tp, c13, c0, 3         @ yes, set TLS register
+        streq   \tp, [\tmp2, #-15]              @ set TLS value at 0xffff0ff0
+        .endm
+
+        .macro set_tls_software, tp, tmp1, tmp2
+        mov     \tmp1, #0xffff0fff
+        str     \tp, [\tmp1, #-15]              @ set TLS value at 0xffff0ff0
+        .endm
+#endif
+
+#ifdef CONFIG_TLS_REG_EMUL
+#define tls_emu         1
+#define has_tls_reg             1
+#define set_tls         set_tls_none
+#elif __LINUX_ARM_ARCH__ >= 7 ||                                        \
+        (__LINUX_ARM_ARCH__ == 6 && defined(CONFIG_CPU_32v6K))
+#define tls_emu         0
+#define has_tls_reg             1
+#define set_tls         set_tls_v6k
+#elif __LINUX_ARM_ARCH__ == 6
+#define tls_emu         0
+#define has_tls_reg             (elf_hwcap & HWCAP_TLS)
+#define set_tls         set_tls_v6
+#else
+#define tls_emu         0
+#define has_tls_reg             0
+#define set_tls         set_tls_software
+#endif
+
+#endif  /* __ASMARM_TLS_H */
diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7ee48e7f8f31..a6cfb1791af3 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -22,6 +22,7 @@
 #include <asm/thread_notify.h>
 #include <asm/unwind.h>
 #include <asm/unistd.h>
+#include <asm/tls.h>
 
 #include "entry-header.S"
 
@@ -739,12 +740,7 @@ ENTRY(__switch_to)
 #ifdef CONFIG_MMU
         ldr     r6, [r2, #TI_CPU_DOMAIN]
 #endif
-#if defined(CONFIG_HAS_TLS_REG)
-        mcr     p15, 0, r3, c13, c0, 3          @ set TLS register
-#elif !defined(CONFIG_TLS_REG_EMUL)
-        mov     r4, #0xffff0fff
-        str     r3, [r4, #-15]                  @ TLS val at 0xffff0ff0
-#endif
+        set_tls r3, r4, r5
 #ifdef CONFIG_MMU
         mcr     p15, 0, r6, c3, c0, 0           @ Set domain register
 #endif
@@ -1009,17 +1005,12 @@ kuser_cmpxchg_fixup:
  */
 
 __kuser_get_tls:                                @ 0xffff0fe0
-
-#if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
-        ldr     r0, [pc, #(16 - 8)]             @ TLS stored at 0xffff0ff0
-#else
-        mrc     p15, 0, r0, c13, c0, 3          @ read TLS register
-#endif
+        ldr     r0, [pc, #(16 - 8)]     @ read TLS, set in kuser_get_tls_init
         usr_ret lr
-
-        .rep    5
-        .word   0                       @ pad up to __kuser_helper_version
-        .endr
+        mrc     p15, 0, r0, c13, c0, 3  @ 0xffff0fe8 hardware TLS code
+        .rep    4
+        .word   0                       @ 0xffff0ff0 software TLS value, then
+        .endr                           @ pad up to __kuser_helper_version
 
 /*
  * Reference declaration:
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 7ae65dc594a4..648c3c1e16c4 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -269,6 +269,21 @@ static void __init cacheid_init(void)
 extern struct proc_info_list *lookup_processor_type(unsigned int);
 extern struct machine_desc *lookup_machine_type(unsigned int);
 
+static void __init feat_v6_fixup(void)
+{
+        int id = read_cpuid_id();
+
+        if ((id & 0xff0f0000) != 0x41070000)
+                return;
+
+        /*
+         * HWCAP_TLS is available only on 1136 r1p0 and later,
+         * see also kuser_get_tls_init.
+         */
+        if ((((id >> 4) & 0xfff) == 0xb36) && (((id >> 20) & 3) == 0))
+                elf_hwcap &= ~HWCAP_TLS;
+}
+
 static void __init setup_processor(void)
 {
         struct proc_info_list *list;
@@ -311,6 +326,8 @@ static void __init setup_processor(void)
         elf_hwcap &= ~HWCAP_THUMB;
 #endif
 
+        feat_v6_fixup();
+
         cacheid_init();
         cpu_proc_init();
 }
diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1621e5327b2a..cda78d59aa31 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -30,6 +30,7 @@
 #include <asm/unistd.h>
 #include <asm/traps.h>
 #include <asm/unwind.h>
+#include <asm/tls.h>
 
 #include "ptrace.h"
 #include "signal.h"
@@ -518,17 +519,20 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 
         case NR(set_tls):
                 thread->tp_value = regs->ARM_r0;
-#if defined(CONFIG_HAS_TLS_REG)
-                asm ("mcr p15, 0, %0, c13, c0, 3" : : "r" (regs->ARM_r0) );
-#elif !defined(CONFIG_TLS_REG_EMUL)
-                /*
-                 * User space must never try to access this directly.
-                 * Expect your app to break eventually if you do so.
-                 * The user helper at 0xffff0fe0 must be used instead.
-                 * (see entry-armv.S for details)
-                 */
-                *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
-#endif
+                if (tls_emu)
+                        return 0;
+                if (has_tls_reg) {
+                        asm ("mcr p15, 0, %0, c13, c0, 3"
+                                : : "r" (regs->ARM_r0));
+                } else {
+                        /*
+                         * User space must never try to access this directly.
+                         * Expect your app to break eventually if you do so.
+                         * The user helper at 0xffff0fe0 must be used instead.
+                         * (see entry-armv.S for details)
+                         */
+                        *((unsigned int *)0xffff0ff0) = regs->ARM_r0;
+                }
                 return 0;
 
 #ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG
@@ -743,6 +747,16 @@ void __init trap_init(void)
         return;
 }
 
+static void __init kuser_get_tls_init(unsigned long vectors)
+{
+        /*
+         * vectors + 0xfe0 = __kuser_get_tls
+         * vectors + 0xfe8 = hardware TLS instruction at 0xffff0fe8
+         */
+        if (tls_emu || has_tls_reg)
+                memcpy((void *)vectors + 0xfe0, (void *)vectors + 0xfe8, 4);
+}
+
 void __init early_trap_init(void)
 {
         unsigned long vectors = CONFIG_VECTORS_BASE;
@@ -761,6 +775,11 @@ void __init early_trap_init(void)
         memcpy((void *)vectors + 0x1000 - kuser_sz, __kuser_helper_start, kuser_sz);
 
         /*
+         * Do processor specific fixups for the kuser helpers
+         */
+        kuser_get_tls_init(vectors);
+
+        /*
          * Copy signal return handlers into the vector page, and
          * set sigreturn to be a pointer to these.
          */
diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 346ae14824a5..71d5d5efceef 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -717,17 +717,6 @@ config TLS_REG_EMUL
           a few prototypes like that in existence) and therefore access to
           that required register must be emulated.
 
-config HAS_TLS_REG
-        bool
-        depends on !TLS_REG_EMUL
-        default y if SMP || CPU_32v7
-        help
-          This selects support for the CP15 thread register.
-          It is defined to be available on some ARMv6 processors (including
-          all SMP capable ARMv6's) or later processors.  User space may
-          assume directly accessing that register and always obtain the
-          expected value only on ARMv7 and above.
-
 config NEEDS_SYSCALL_FOR_CMPXCHG
         bool
         help
diff --git a/arch/arm/mm/proc-v6.S b/arch/arm/mm/proc-v6.S
index 7a5337ed7d68..2f5a3c23a0fe 100644
--- a/arch/arm/mm/proc-v6.S
+++ b/arch/arm/mm/proc-v6.S
@@ -239,7 +239,8 @@ __v6_proc_info:
         b       __v6_setup
         .long   cpu_arch_name
         .long   cpu_elf_name
-        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA
+        /* See also feat_v6_fixup() for HWCAP_TLS */
+        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_JAVA|HWCAP_TLS
         .long   cpu_v6_name
         .long   v6_processor_functions
         .long   v6wbi_tlb_fns
@@ -262,7 +263,7 @@ __pj4_v6_proc_info:
         b       __v6_setup
         .long   cpu_arch_name
         .long   cpu_elf_name
-        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP
+        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
         .long   cpu_pj4_name
         .long   v6_processor_functions
         .long   v6wbi_tlb_fns
diff --git a/arch/arm/mm/proc-v7.S b/arch/arm/mm/proc-v7.S
index 7aaf88a3b7aa..8071bcd4c995 100644
--- a/arch/arm/mm/proc-v7.S
+++ b/arch/arm/mm/proc-v7.S
@@ -344,7 +344,7 @@ __v7_proc_info:
         b       __v7_setup
         .long   cpu_arch_name
         .long   cpu_elf_name
-        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP
+        .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP|HWCAP_TLS
         .long   cpu_v7_name
         .long   v7_processor_functions
         .long   v7wbi_tlb_fns