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>

3 files changed, 54 insertions, 27 deletions

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.
          */